Momentum distribution n(k) implementation is missing in the batched VMC/DMC

[aannabe]

When working on a Fermi surface of a delafossite, I noticed that it requires quite a lot of n(k) samples. Currently, the CPU version works but having the GPU version would be greatly beneficial for extra resources.

[prckent]

After discussing with Peter, he pointed out that this is implemented in the batched code in https://github.com/QMCPACK/qmcpack/pull/3447 . More optimization may be needed to fully use the multiwalker infrastructure and gain further speedups, but it is worth kicking the tires. Jaron did significant testing in that PR.

[prckent]

@aannabe let us know what you find. I am not sure if, e.g. NEXUS will drive this batched observable or if a small update is needed.

[aannabe]

Using Nexus with driver = 'batched', currently puts the momentum estimator in the hamiltonian section. This will run but silently not accumulate the n(k):

h5ls vmc_gc.s000.stat.h5 

ElecElec                 Group
IonIon                   Group
KEcorr                   Group
Kinetic                  Group
LocalECP                 Group
LocalEnergy              Group
LocalEnergy_sq           Group
LocalPotential           Group
MPC                      Group
NonLocalECP              Group

I was told that it needs to go to qmc section. Doing so results in a crash with the following error:

Fatal Error. Aborting at EstimatorManager input:unparsable <estimator> node, name: momentum type: momentum in Estimators input.

The above were run on Summit, and inputs are attached. Any ideas?

batched_nk.zip

[jtkrogel]

@aannabe please can you retry your problem case by basing your input off of the following example:

https://github.com/QMCPACK/qmcpack/blob/develop/nexus/examples/qmcpack/rsqmc_quantum_espresso/01_diamond_dft_vmc/diamond_lda_vmc_batched_estimators.py

The momentum distribution was given a different name for the batched drivers.

[aannabe]

Thank you, a quick calculation of Gamma point using the above Nexus example runs successfully:

h5ls vmc_batched.s000.stat.h5

ElecElec                 Group
IonIon                   Group
Kinetic                  Group
LocalECP                 Group
LocalEnergy              Group
LocalEnergy_sq           Group
LocalPotential           Group
MPC                      Group
NonLocalECP              Group
nofk                     Group

Closing the issue.