DMC Forces¶

Calculating atomic forces in DMC allows for geometry optimization and vibrational analysis at the QMC level.

Overview¶

Force calculations in DMC are more expensive than energy calculations alone because they require computing the gradient of the energy with respect to nuclear coordinates.

Configuration¶

To enable force calculations, you typically need to: 1. Enable force computation in the input. 2. Ensure that the pseudopotentials (if used) support force calculations.

Example¶

%module opt_geo
    ...
    iforce_analy        1   # Analytic forces
    alfgeo              0.5 # Force step size
%endmodule

Output file¶

The forces are written to force_analytic in the working directory. Name the file yourself when more than one run shares a directory -- a VMC and a DMC run, say -- so that they do not overwrite each other:

%module outputs
    file_force_analytic  'force_dmc.dat'
%endmodule

Outputs Keywords

Check tests/CI_test/VMC-C4H6-ci44_pVQZ_20_dets_12_csf_optall/vmc_optall_ci44.inp for VMC force examples, which often translate to DMC.