In section 
results are presented for VMC
calculations performed using both the Ewald interaction and the new
interaction. To provide the fairest possible comparison of the two
interactions, the trial wavefunctions for each calculation were
optimised, using the variance minimisation technique described in
chapter , with respect to the Hamiltonian to be
used in the subsequent VMC calculation. This enables both
calculations to be performed using the optimal values of the
variational parameters in the wavefunction for the given Hamiltonian.
The standard expression for the intrinsic variance
was used. The form of 
was chosen to match the form to be used
in the VMC calculation. For the calculations using the Ewald
interaction, 
was chosen to be
For the calculations using the new electron-electron interaction,
was chosen to be
In both cases, the electron configurations are still fixed throughout the optimisation process. Therefore the total electron-electron energy for each configuration is still just calculated once and stored throughout the optimisation procedure.