Another significant advantage of the optimisation procedure of
Eq.(
) is that new functions such as 
can be tested
without actually having to implement them into the mainstream solid
VMC code. All one has to be able to do is calculate 
and
for each configuration. The optimisation of Eq.()
can then be performed to see if the proposed new function produces an
improvement in the quality of 
, i.e. a reduction in the energy and
variance of the energy. To calculate the new value for with
included, the Jastrow factor in Eq.() is written as
where the sum over pairs of electrons is performed by storing lists of which electrons are within L of each ion. The intention was to then update these lists whenever an electron was moved in the VMC calculation.
To calculate the new value of the kinetic energy with included in
the wavefunction, the gradient and Laplacian of the new also need
to be calculated. This was done in a similar way to Eq.(), by summing the contributions to the gradient and Laplacian of
from each ion in the solid.
