It is clear from the previous section that the optimisation procedure, Eq.(), produces a trial wavefunction, , that has a VMC energy significantly closer to the DMC energy. However, there is still room for improvement (about 0.37 eV per atom). It was therefore decided to attempt to optimise another part of the trial/guiding wavefunction, Eq.() to see if the VMC energy could be reduced still further. The most obvious candidate for further optimisation was the Jastrow function as this also has a form in which optimisation of a relatively small set of parameters can be performed.