If the intention is to use variance minimisation and then VMC as an
initial guide to performing more accurate DMC calculations then the
situation is not so clear cut. Only the variance of the expectation
value of an operator is dependent on the quality of the guiding
wavefunction, not the expectation value itself.
It is therefore not
necessary to perform the optimisation to the same level of accuracy as
for the VMC calculation. Indeed, the optimisation process can be more
computationally expensive than the DMC run itself. This balance in
effort spent on optimising the initial trial/guiding wavefunction
versus time spent performing actual calculations will be returned to
in chapter 
, where DMC calculations are
performed on a series of systems describing excited states without the
need for re-optimising the wavefunction for each system.