In chapter 
, the two QMC methods used for the
calculations in the rest of this thesis, the Variational quantum Monte
Carlo (VMC) and Diffusion quantum Monte Carlo (DMC) method are
introduced. Details of the algorithms used to implement these methods
on serial and parallel computers are given.
In chapter , the specific details of how to
perform a QMC calculation on a solid using the supercell technique are
given. The choice of wavefunction and evaluation of Coulomb
interactions are discussed.
Chapter describes our application of the variance
minimisation, optimisation technique to the problem of producing
trial/guiding wavefunctions for use in QMC calculations of solids.
Again details are given of the algorithm used and how to implement it
on both serial and parallel computers. New functional forms of
wavefunction are introduced, that yield comparable if not improved
accuracy over traditional functional forms, are more suitable for
optimisation and are considerably faster to evaluate within a QMC
code.
Chapter describes new forms of electron-electron
interaction that are designed to dramatically reduce the troublesome
Coulomb finite size effects present in QMC supercell calculations.
The technical advances made to the QMC technique described in
chapters and are brought
together in chapter to enable us to attempt a
new application of QMC - the calculation of excitation energies. Two
separate methods of evaluating excitation energies within QMC are, (i)
the addition and subtraction of electrons and (ii) the promotion of
electrons. Both these techniques require energies to be evaluated to
at least an order of magnitude higher accuracy than previous QMC
calculations. The results obtained from the two techniques are
compared both with each other and with the results of more established
electronic structure techniques.
Finally, in chapter , some conclusions on the
work are drawn.