Input File Description

a string describing the task to be performed:
'scf', 'nscf', 'bands', 'phonon', 'relax', 'md',
'vc-relax', 'vc-md', 'neb', 'smd', 'metadyn'
(vc = variable-cell).
         

reprinted on output.
         

'high' | 'default' | 'low' | 'minimal'
         

'from_scratch'  : from scratch
                  NEB and SMD only: the starting path is obtained
                  with a linear interpolation between the images
                  specified in the ATOMIC_POSITIONS card.
                  Note that in the linear interpolation
                  periodic boundary conditions ARE NON USED.

'restart'       : from previous interrupted run
         

This flag controls the way wavefunctions are stored to disk :

.TRUE.  collect wavefunctions from all processors and store
        them into the output data directory outdir/prefix.save

.FALSE. do not collect wavefunctions, leave them in temporary
        local files (one per processor). The resulting format
        will be readable only by jobs running on the same
        number of processors and pools. Useful if you do not
        need the wavefunction or if you want to reduce the I/O
        or the disk occupancy.
         

number of ionic + electronic steps
         

band energies are written every iprint iterations
         

calculate stress. It is set to .TRUE. automatically if
calculation='vc-md' or 'vc-relax'
         

print forces. Set to .TRUE. if calculation='relax','md','vc-md'
         

time step for molecular dynamics, in Rydberg atomic units
(1 a.u.=4.8378 * 10^-17 s : beware, CP and FPMD codes use
 Hartree atomic units, half that much!!!)
         

input, temporary, output files are found in this directory,
see also 'wfcdir'
         

this directory specifies where to store files generated by
each processor (*.wfc{N}, *.igk{N}, etc.). The idea here is
to be able to separately store the largest files, while
the files necessary for restarting still go into 'outdir'
(for now only works for stand alone PW )
         

prepended to input/output filenames:
prefix.wfc, prefix.rho, etc.
         

If .false. it does not open a subdirectory for each k_point
in the prefix.save directory.
         

jobs stops after max_seconds CPU time
         

convergence threshold on total energy (a.u) for ionic
minimization: the convergence criterion is satisfied
when the total energy changes less than etot_conv_thr
between two consecutive scf steps.
See also forc_conv_thr - both criteria must be satisfied
         

convergence threshold on forces (a.u) for ionic
minimization: the convergence criterion is satisfied
when all components of all forces are smaller than
forc_conv_thr.
See also etot_conv_thr - both criteria must be satisfied
         

Specifies the amount of disk I/O activity
'high':    save all data at each SCF step

'default': save wavefunctions at each SCF step unless
           there is a single k-point per process

'low' :    store wfc in memory, save only at the end

'none':    do not save wfc, not even at the end

If restarting from an interrupted calculation, the code
will try to figure out what is available on disk. The
more you write, the more complete the restart will be.
         

directory containing pseudopotential files
         

If .TRUE. a sawlike potential simulating an electric field
is added to the bare ionic potential. See variables
edir, eamp, emaxpos, eopreg for the form and size of
the added potential.
         

If .TRUE. and tefield=.TRUE. a dipole correction is also
added to the bare ionic potential - implements the recipe
of L. Bengtsson, PRB 59, 12301 (1999). See variables edir,
emaxpos, eopreg for the form of the correction, that must
be used only in a slab geometry, for surface calculations,
with the discontinuity in the empty space.
         

If .TRUE. a homogeneous finite electric field described
through the modern theory of the polarization is applied.
This is different from "tefield=.true." !
         

If .TRUE. perform a Berry phase calculation
See the header of PW/bp_c_phase.f90 for documentation
         

For Berry phase calculation: direction of the k-point
strings in reciprocal space. Allowed values: 1, 2, 3
1=first, 2=second, 3=third reciprocal lattice vector
For calculations with finite electric fields
(lelfield==.true.), gdir is the direction of the field
         

For Berry phase calculation: number of k-points to be
calculated along each symmetry-reduced string
The same for calculation with finite electric fields
(lelfield==.true.)
         

In the case of a finite electric field  ( lelfield == .TRUE. )
it defines the number of iterations for converging the
wavefunctions in the electric field Hamiltonian, for each
external iteration on the charge density
         

Bravais-lattice index:

  ibrav        structure                   celldm(2)-celldm(6)

    0          "free", see above                 not used
    1          cubic P (sc)                      not used
    2          cubic F (fcc)                     not used
    3          cubic I (bcc)                     not used
    4          Hexagonal and Trigonal P        celldm(3)=c/a
    5          Trigonal R                      celldm(4)=cos(alpha)
    6          Tetragonal P (st)               celldm(3)=c/a
    7          Tetragonal I (bct)              celldm(3)=c/a
    8          Orthorhombic P                  celldm(2)=b/a,celldm(3)=c/a
    9          Orthorhombic base-centered(bco) celldm(2)=b/a,celldm(3)=c/a
   10          Orthorhombic face-centered      celldm(2)=b/a,celldm(3)=c/a
   11          Orthorhombic body-centered      celldm(2)=b/a,celldm(3)=c/a
   12          Monoclinic P                    celldm(2)=b/a,celldm(3)=c/a,
                                               celldm(4)=cos(ab)
   13          Monoclinic base-centered        celldm(2)=b/a,celldm(3)=c/a,
                                               celldm(4)=cos(ab)
   14          Triclinic                       celldm(2)= b/a,
                                               celldm(3)= c/a,
                                               celldm(4)= cos(bc),
                                               celldm(5)= cos(ac),
                                               celldm(6)= cos(ab)

For P lattices: the special axis (c) is the z-axis, one basal-plane
vector (a) is along x, the other basal-plane vector (b) is at angle
gamma for monoclinic, at 120 degrees for trigonal and hexagonal
lattices, at 90 degrees for cubic, tetragonal, orthorhombic lattices

sc simple cubic
====================
v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,1)

fcc face centered cubic
====================
v1 = (a/2)(-1,0,1),  v2 = (a/2)(0,1,1), v3 = (a/2)(-1,1,0).

bcc body entered cubic
====================
v1 = (a/2)(1,1,1),  v2 = (a/2)(-1,1,1),  v3 = (a/2)(-1,-1,1).

simple hexagonal and trigonal(p)
====================
v1 = a(1,0,0),  v2 = a(-1/2,sqrt(3)/2,0),  v3 = a(0,0,c/a).

trigonal(r)
===================
for these groups, the z-axis is chosen as the 3-fold axis, but the
crystallographic vectors form a three-fold star around the z-axis,
and the primitive cell is a simple rhombohedron. The crystallographic
vectors are:
      v1 = a(tx,-ty,tz),   v2 = a(0,2ty,tz),   v3 = a(-tx,-ty,tz).
where c=cos(alpha) is the cosine of the angle alpha between any pair
of crystallographic vectors, tc, ty, tz are defined as
     tx=sqrt((1-c)/2), ty=sqrt((1-c)/6), tz=sqrt((1+2c)/3)

simple tetragonal (p)
====================
   v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,c/a)

body centered tetragonal (i)
================================
   v1 = (a/2)(1,-1,c/a),  v2 = (a/2)(1,1,c/a),  v3 = (a/2)(-1,-1,c/a).

simple orthorhombic (p)
=============================
   v1 = (a,0,0),  v2 = (0,b,0), v3 = (0,0,c)

bco base centered orthorhombic
=============================
   v1 = (a/2,b/2,0),  v2 = (-a/2,b/2,0),  v3 = (0,0,c)

face centered orthorhombic
=============================
   v1 = (a/2,0,c/2),  v2 = (a/2,b/2,0),  v3 = (0,b/2,c/2)

body centered orthorhombic
=============================
   v1 = (a/2,b/2,c/2),  v2 = (-a/2,b/2,c/2),  v3 = (-a/2,-b/2,c/2)

monoclinic (p)
=============================
   v1 = (a,0,0), v2= (b*cos(gamma), b*sin(gamma), 0),  v3 = (0, 0, c)
where gamma is the angle between axis a and b

base centered monoclinic
=============================
   v1 = (  a/2,         0,                -c/2),
   v2 = (b*cos(gamma), b*sin(gamma), 0),
   v3 = (  a/2,         0,                  c/2),
where gamma is the angle between axis a and b

triclinic
=============================
   v1 = (a, 0, 0),
   v2 = (b*cos(gamma), b*sin(gamma), 0)
   v3 = (c*cos(beta),  c*(cos(alpha)-cos(beta)cos(gamma))/sin(gamma),
         c*sqrt( 1 + 2*cos(alpha)cos(beta)cos(gamma)
                   - cos(alpha)^2-cos(beta)^2-cos(gamma)^2 )/sin(gamma) )
where alpha is the angle between axis b and c
       beta is the angle between axis a and c
      gamma is the angle between axis a and b
         

Crystallographic constants - see description of ibrav variable.

* alat = celldm(1) is the lattice parameter "a" (in BOHR)
* only needed celldm (depending on ibrav) must be specified
* if ibrav=0 only alat = celldm(1) is used (if present)
         

number of atoms in the unit cell
         

number of types of atoms in the unit cell
         

number of electronic states (bands) to be calculated.
Note that in spin-polarized calculations the number of
k-point, not the number of bands per k-point, is doubled
         

number of electron in the unit cell
(may be noninteger if you wish)

A compensating jellium background is inserted
to remove divergences if the cell is not neutral
         

total system charge. Used only if nelec is unspecified,
otherwise it is ignored.
         

kinetic energy cutoff (Ry) for wavefunctions
         

kinetic energy cutoff (Ry) for charge density and potential
If there are ultrasoft PP, a larger value than the default is
often desirable (ecutrho = 8 to 12 times ecutwfc, typically).
If all PP are norm-conserving, you should stick to the default;
you may reduce it to spare time, but not by a large amount.
         

if (.TRUE.) symmetry is not used. Note that a k-point grid
provided in input is used "as is"; an automatically generated
k-point grid will contain only points in the irreducible BZ
of the lattice.  Use with care in low-symmetry large cells
if you cannot afford a k-point grid with the correct symmetry.
         

if(.TRUE.) symmetry is not used but the k-points are
forced to have the symmetry of the Bravais lattice;
an automatically generated k-point grid will contain
all the k-points of the grid and the points rotated by
the symmetries of the Bravais lattice which are not in the
original grid. If available, time reversal is
used to reduce the k-points (and the q => -q symmetry
is used in the phonon code). To disable also this symmetry set
noinv=.TRUE..
         

if (.TRUE.) disable the usage of time reversal (q => -q)
symmetry in k-point generation
         

if (.TRUE.) force the symmetry group to be symmorphic by disabling
symmetry operations having an associated fractionary translation
         

'smearing':     gaussian smearing for metals
                requires a value for degauss

'tetrahedra' :  for metals and DOS calculation
                (see PRB49, 16223 (1994))
                Requires uniform grid of k-points,
                automatically generated (see below)
                Not suitable (because not variational) for
                force/optimization/dynamics calculations

'fixed' :       for insulators with a gap

'from_input' :  The occupation are read from input file.
                Presently works only with one k-point
                (LSDA allowed).
         

value of the gaussian spreading (Ry) for brillouin-zone
integration in metals.
         

'gaussian', 'gauss':
    ordinary Gaussian spreading (Default)

'methfessel-paxton', 'm-p', 'mp':
    Methfessel-Paxton first-order spreading
    (see PRB 40, 3616 (1989)).

'marzari-vanderbilt', 'cold', 'm-v', 'mv':
    Marzari-Vanderbilt cold smearing
    (see PRL 82, 3296 (1999))

'fermi-dirac', 'f-d', 'fd':
    smearing with Fermi-Dirac function
         

nspin = 1 :  non-polarized calculation (default)

nspin = 2 :  spin-polarized calculation, LSDA
             (magnetization along z axis)

nspin = 4 :  spin-polarized calculation, noncollinear
             (magnetization in generic direction)
             DO NOT specify nspin in this case;
             specify "noncolin=.TRUE." instead
         

if .true. the program will perform a noncollinear calculation.
         

starting spin polarization (values between -1 and 1)
on atomic type 'i' in a spin-polarized calculation.
Breaks the symmetry and provides a starting point for
self-consistency. The default value is zero, BUT a value
MUST be specified for AT LEAST one atomic type in spin
polarized calculations. Note that if start from zero
initial magnetization, you will get zero final magnetization
in any case. If you desire to start from an antiferromagnetic
state, you may need to define two different atomic species
corresponding to sublattices of the same atomic type.
If you fix the magnetization with "nelup/neldw" or with
"multiplicity" or with "tot_magnetization", you should
not specify starting_magnetization.
If you are restarting from a previous run, or from an
interrupted run, starting_magnetization is ignored.
         

spin multiplicity (2s+1). 1 is singlet, 2 for doublet etc.
Note that this fixes the final value of the magnetization.
if unspecified or a non-zero value is specified in nelup/neldw
then multiplicity variable is ignored.
Do not specify both multiplicity and tot_magnetization.
         

majority spin - minority spin (nelup - neldw).
if unspecified or a non-zero value is specified in nelup/neldw
then tot_magnetization variable is ignored.
Do not specify both multiplicity and tot_magnetization.
YES, there is redundancy! nelup/neldw are enough to specify
the spin state. However these variables are not very convenient
and will be eliminated from the input in future versions.
It is recommended to use either 'multiplicity' or equivalently
'tot_magnetization' to specify the spin state.
         

ecfixed, qcutz, q2sigma:  parameters for modified functional to be
used in variable-cell molecular dynamics (or in stress calculation).
"ecfixed" is the value (in Rydberg) of the constant-cutoff;
"qcutz" and "q2sigma" are the height and the width (in Rydberg)
of the energy step for reciprocal vectors whose square modulus
is greater than "ecfixed". In the kinetic energy, G^2 is
replaced by G^2 + qcutz * (1 + erf ( (G^2 - ecfixed)/q2sigma) )
See: M. Bernasconi et al, J. Phys. Chem. Solids 56, 501 (1995)
         

Exchange-correlation functional: eg 'PBE', 'BLYP' etc
See Modules/functionals.f90 for allowed values.
Overrides the value read from pseudopotential files.
Use with care and if you know what you are doing!
         

lda_plus_u, Hubbard_alpha(i), Hubbard_U(i): parameters for LDA+U
calculations If lda_plus_u = .TRUE. you must specify, for species i,
the parameters U and (optionally) alpha of the Hubbard model (both in eV).
See: Anisimov, Zaanen, and Andersen, PRB 44, 943 (1991); Anisimov
et al., PRB 48, 16929 (1993); Liechtenstein, Anisimov, and Zaanen, PRB
52, R5467 (1994); Cococcioni and de Gironcoli, PRB 71, 035105 (2005).
         

In the first iteration of an LDA+U run it overwrites
the m-th eigenvalue of the ns occupation matrix for the
ispin component of atomic species I. Leave unchanged
eigenvalues that are not set. This is useful to suggest
the desired orbital occupations when the default choice
takes another path.
         

Only active when lda_plus_U is .true., specifies the type
of projector on localized orbital to be used in the LDA+U
scheme.

Currently available choices:
'atomic': use atomic wfc's (as they are) to build the projector

'ortho-atomic': use Lowdin orthogonalized atomic wfc's

'norm-atomic':  Lowdin normalization of atomic wfc. Keep in mind:
                atomic wfc are not orthogonalized in this case.
                This is a "quick and dirty" trick to be used when
                atomic wfc from the pseudopotential are not
                normalized (and thus produce occupation whose
                value exceeds unity). If orthogonalized wfc are
                not needed always try 'atomic' first.

'file':         use the information from file "prefix".atwfc that must
                have been generated previously, for instance by pmw.x
                (see PP/poormanwannier.f90 for details)

NB: forces and stress currently implemented only for the
'atomic' choice.
         

The direction of the electric field or dipole correction is
parallel to the bg(:,edir) reciprocal lattice vector, so the
potential is constant in planes defined by FFT grid points;
edir = 1, 2 or 3. Used only if tefield is .TRUE.
         

Position of the maximum of the sawlike potential along crystal
axis "edir", within the  unit cell (see below), 0 < emaxpos < 1
Used only if tefield is .TRUE.
         

Zone in the unit cell where the sawlike potential decreases.
( see below, 0 < eopreg < 1 ). Used only if tefield is .TRUE.
         

Amplitude of the electric field (in a.u. = 51.44 10^10 V/m )
The sawlike potential increases with slope "eamp" in the
region from (emaxpos+eopreg-1) to (emaxpos), then decreases
to 0 until (emaxpos+eopreg), in units of the crystal
vector "edir". Important: the change of slope of this
potential must be located in the empty region, or else
unphysical forces will result. Used only if tefield is .TRUE.
         

The angle expressed in degrees between the initial
magnetization and the z-axis. For noncollinear calculations
only; index i runs over the atom types.
         

The angle expressed in degrees between the projection
of the initial magnetization on x-y plane and the x-axis.
For noncollinear calculations only.
         

Used to perform constrained calculations in magnetic systems.
Currently available choices:

'none':
         no constraint

'total':
         total magnetization is constrained
         If nspin=4 (noncolin=.True.) constraint is imposed by
         adding a penalty functional to the total energy:

         LAMBDA * SUM_{i} ( magnetization(i) - fixed_magnetization(i) )**2

         where the sum over i runs over the three components of
         the magnetization. Lambda is a real number (see below).
         If nspin=2 constraint is imposed by defining two Fermi
         energies for spin up and down.
         Only fixed_magnetization(3) can be defined in this case.

'atomic':
         atomic magnetization are constrained to the defined
         starting magnetization adding a penalty:

         LAMBDA * SUM_{i,itype} ( magnetic_moment(i,itype) - mcons(i,itype) )**2

         where i runs over the cartesian components (or just z
         in the collinear case) and itype over the types (1-ntype).
         mcons(:,:) array is defined from starting_magnetization,
         (and angle1, angle2 in the non-collinear case). lambda is
         a real number

'total direction':
          the angle theta of the total magnetization
          with the z axis (theta = fixed_magnetization(3))
          is constrained:

          LAMBDA * ( magnetization(1) - magnetization(3)*tan(theta) )**2

'atomic direction':
          not all the components of the atomic
          magnetic moment are constrained but only the cosine
          of angle1, and the penalty functional is:

          LAMBDA * SUM_{itype} ( mag_mom(3,itype)/mag_mom_tot - cos(angle1(ityp)) )**2
         

value of the total magnetization to be maintained fixed when
constrained_magnetization='total'
         

parameter used for constrained_magnetization calculations
NB: LAMBDA is reduced in the first iterations and is increased
    slowly up to the input value.
         

It is the number of iterations after which the program
write all the atomic magnetic moments.
         

if .TRUE. the noncollinear code can use a pseudopotential with
spin-orbit.
         

if .TRUE. the system is assumed to be isolated (a molecule or cluster
in a supercell) and the Makov-Payne correction to the total energy is
computed. An estimate of the vacuum level is also calculated so that
eigenvalues can be properly aligned.
         

if .TRUE. the system is embedded the electrostatic environment
described in the EE namelist.
         

if .TRUE. compute semi-empirical dispersion term (DFT-D).
See S. Grimme, J. Comp. Chem. 27, 1787 (2006), and
V. Barone et al., J. Comp. Chem. 30, 934 (2009).
         

global scaling parameter for DFT-D. Default is good for PBE.
         

cutoff radius (a.u.) for dispersion interactions
         

maximum number of iterations in a scf step
         

Convergence threshold for selfconsistency:
estimated energy error < conv_thr
         

'plain' :    charge density Broyden mixing

'TF' :       as above, with simple Thomas-Fermi screening
            (for highly homogeneous systems)

'local-TF':  as above, with local-density-dependent TF screening
             (for highly inhomogeneous systems)
         

mixing factor for self-consistency
         

number of iterations used in mixing scheme
         

For LDA+U : number of iterations with fixed ns ( ns is the
  atomic density appearing in the Hubbard term ).
         

'david':  Davidson iterative diagonalization with overlap matrix
          (default). Fast, may in some rare cases fail.

'cg' :    conjugate-gradient-like band-by-band diagonalization
          Typically slower than 'david' but it uses less memory
          and is more robust (it seldom fails)

'cg-serial' : as above, do not use the parallel subspace
          diagonalization (see below) between iterations,
          but only serial diagonalization (for testing purposes)

'david-serial': do not use parallel subspace diagonalization
          in Davidson algorithm (for testing purposes).
          The subspace diagonalization in Davidson is performed
          by a fully distributed-memory parallel algorithm on
          4 or more processors, by default. The allocated memory
          scales down with the number of procs. Procs involved
          in diagonalization can be changed with input parameter
          "ortho_para". On multicore CPUs often it is convenient
          to let only one core per CPU to work on linear algebra.
         

meaningful for diagonalization='david' and parallel executables.
The number of processors to be used for the parallel subspace
diagonalization algorithm. With the default value (0) the code
tries to use as many processors as available. Note that the
algorithm uses a square number of processors (4, 9, 16, 25,...),
so the actual number of processors used will be the largest
square number less or equal to ortho_para (if set) or to the
total number of processors (if ortho_para is not set).
         

Convergence threshold for the first iterative diagonalization
(the check is on eigenvalue convergence).
For scf calculations, the default is 1.D-2 if starting from a
superposition of atomic orbitals; 1.D-5 if starting from a
charge density. During self consistency the threshold (ethr)
is automatically reduced when approaching convergence.
For non-scf calculations, this is the threshold used in the
iterative diagonalization. The default is conv_thr / nelec.
For 'phonon' calculations, diago_thr_init is ignored:
the threshold is always set to  conv_thr / nelec .
         

For conjugate gradient diagonalization:
max number of iterations
         

For Davidson diagonalization: dimension of workspace
(number of wavefunction packets, at least 2 needed).
A larger value may yield a faster algorithm but uses
more memory
         

If .TRUE. all the empty states are diagonalized at the same level
of accuracy of the occupied ones. Otherwise the empty states are
diagonalized using a larger threshold (this should not affect
total energy, forces, and other ground-state properties).
         

For finite electric field calculations (lelfield == .TRUE.),
it defines the intensity of the field in a.u.
         

'atomic': starting potential from atomic charge superposition
          ( default for scf, *relax, *md, neb, smd )

'file'  : start from existing "charge-density.xml" file
          ( default, only possibility for nscf, bands )
         

'atomic': start from superposition of atomic orbitals
          If not enough atomic orbitals are available,
          fill with random numbers the remaining wfcs
          The scf typically starts better with this option,
          but in some high-symmetry cases one can "loose"
          valence states, ending up in the wrong ground state.

'atomic+random': as above, plus a superimposed "randomization"
          of atomic orbitals. Prevents the "loss" of states
          mentioned above.

'random': start from random wfcs. Slower start of scf but safe.
          It may also reduce memory usage in conjunction with
          diagonalization='cg'

'file':   start from a wavefunction file
         

If .true., use the real-space algorithm for augmentation
charges in ultrasoft pseudopotentials.
Must faster execution of ultrasoft-related calculations,
but numerically less accurate than the default algorithm.
Use with care and after testing!
         

Specify the type of ionic dynamics.

For constrained dynamics or constrained optimisations add the
CONSTRAINTS card (when the card is present the SHAKE algorithm is
                  automatically used).

For different type of calculation different possibilities are
allowed and different default values apply:

CASE ( calculation = 'relax' )
    'bfgs' :   (default)   use BFGS quasi-newton algorithm,
                           based on the trust radius procedure,
                           for structural relaxation
    'damp' :               use damped (quick-min Verlet)
                           dynamics for structural relaxation

CASE ( calculation = 'md' )
    'verlet' : (default)   use Verlet algorithm to integrate
                           Newton's equation
    'langevin'             ion dynamics is over-damped Langevin

CASE ( calculation = 'vc-relax' )
    'bfgs' :   (default)   use BFGS quasi-newton algorithm;
                           cell_dynamics must be 'bfgs' too
    'damp' :               use damped (Beeman) dynamics for
                           structural relaxation
CASE ( calculation = 'vc-md' )
    'beeman' : (default)   use Beeman algorithm to integrate
                           Newton's equation
         

'default '  : if restarting, use atomic positions read from the
              restart file; in all other cases, use atomic
              positions from standard input.

'from_input' : restart the simulation with atomic positions read
              from standard input, even if restarting.
         

'full' :           the full phase-space is used for the ionic
                   dynamics.

'coarse-grained' : a coarse-grained phase-space, defined by a set
                   of constraints, is used for the ionic dynamics
                   (used for calculation of free-energy barriers)
         

Used to extrapolate the potential from preceding ionic steps.

'none'        :  no extrapolation

'atomic'      :  extrapolate the potential as if it was a sum of
                 atomic-like orbitals

'first_order' :  extrapolate the potential with first-order
                 formula

'second_order':  as above, with second order formula
         

 Used to extrapolate the wavefunctions from preceding ionic steps.

'none'        :  no extrapolation

'first_order' :  extrapolate the wave-functions with first-order
                 formula - NOT IMPLEMENTED WITH USPP

'second_order':  as above, with second order formula
                 NOT IMPLEMENTED WITH USPP
         

This keyword is useful when simulating the dynamics and/or the
thermodynamics of an isolated system. If set to true the total
torque of the internal forces is set to zero by adding new forces
that compensate the spurious interaction with the periodic
images. This allows for the use of smaller supercells.

BEWARE: since the potential energy is no longer consistent with
the forces (it still contains the spurious interaction with the
repeated images), the total energy is not conserved anymore.
However the dynamical and thermodynamical properties should be
in closer agreement with those of an isolated system.
Also the final energy of a structural relaxation will be higher,
but the relaxation itself should be faster.
         

Specify the type of dynamics for the cell.
For different type of calculation different possibilities
are allowed and different default values apply:

CASE ( calculation = 'vc-relax' )
  'none':    no dynamics
  'sd':      steepest descent ( not implemented )
  'damp-pr': damped (Beeman) dynamics of the Parrinello-Rahman
             extended lagrangian
  'damp-w':  damped (Beeman) dynamics of the new Wentzcovitch
             extended lagrangian
  'bfgs':    BFGS quasi-newton algorithm (default)
             ion_dynamics must be 'bfgs' too
CASE ( calculation = 'vc-md' )
  'none':    no dynamics
  'pr':      (Beeman) molecular dynamics of the Parrinello-Rahman
             extended lagrangian
  'w':       (Beeman) molecular dynamics of the new Wentzcovitch
             extended lagrangian
         

Target pressure [KBar] in a variable-cell md or relaxation run.
         

Fictitious cell mass [amu] for variable-cell simulations
(both 'vc-md' and 'vc-relax')
         

Used in the construction of the pseudopotential tables.
It should exceed the maximum linear contraction of the
cell during a simulation.
         

Convergence threshold on the pressure for variable cell
relaxation ('vc-relax' : note that the other convergence
thresholds for ionic relaxation apply as well).
         

Select which of the cell parameters should be moved:

all     = all axis and angles are moved
x       = only the x axis is moved
y       = only the y axis is moved
z       = only the z axis is moved
xy      = only the x and y axis are moved, angles are unchanged
xz      = only the x and z axis are moved, angles are unchanged
yz      = only the y and z axis are moved, angles are unchanged
xyz     = x, y and z axis are moved, angles are unchanged
xyt     = x1, x2, y2 (i.e. lower xy triangle of the 2 vectors)
xys     = x1, y1, x2, y2 (i.e. xy square of the 2 vectors)
xyzt    = x1, x2, y2, x3, y3, z3 (i.e. lower xyz triangle of
          the 3 vectors)
         

For single-mode phonon calculation : modenum is the index of the
irreducible representation (irrep) into which the reducible
representation formed by the 3*nat atomic displacements are
decomposed in order to perform the phonon calculation.
         

q-point (units 2pi/a) for phonon calculation.
         

'dcc' : density counter charge correction.
        The electrostatic problem is solved in open boundary
        conditions. At variance with the Makov-Payne approach
        that only estimates an energy correction here the
        scf potential is corrected as well.
        Theory described in:
        I.Dabo, B.Kozinsky, N.E.Singh-Miller and N.Marzari,
        "Electrostatic periodic boundary conditions and
        real-space corrections", Phys.Rev.B 77, 115139 (2008)
         

kinetic energy cutoff defining the grid used for
the open boundary correction.
         

scf mixing parameter for the correcting potential.
         

the correcting potential is updated (mixed) every
n_charge_compensation iteration only.
         

inclusion of dcc correction begins when scf convergence
is better than comp_thr.
         

number of depth levels used by the multigrid solver.