[Feature] update walkers overlap before computing local energy

[jiangtong1000]

ipie/ipie/estimators/energy.py

Lines 134 to 135 in b9973b6

	def compute_estimator(self, system, walkers, hamiltonian, trial, istep=1):
	trial.calc_greens_function(walkers)

Here we should have walkers.ovlp = trial.calc_greens_function(walkers) to update the ovlp too

[linusjoonho]

@jiangtong1000 Could you create a branch which implements the proposed fix and create a pull request?

[fdmalone]

Wait, why? I'm a little worried we're assuming something about the state of the walkers overlap now (although we probably were before). This function should be renamed calculate_energy_and_update_walkers_overlap and documented. I'm sort of against having estimators modify the state of the walker, it seems dangerous. Do we recompute the overlap before propagation?

[linusjoonho]

@fdmalone @jiangtong1000 I actually remember this bug now. The way I fixed last time was to compute overlap consistently in the end of the propagation function. @jiangtong1000 could you not achieve what you wanted to do by evaluating overlap properly in the propagator?

[fdmalone]

I relabelled as it's not a bug but a dangerous implementation feature we should try to document as part of some developer documentation.