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Periodic Systems and Forces

This tutorial demonstrates a VMC calculation for a periodic system (likely LiF based on the title Test LiF, though the folder says Hlattice) computing atomic forces.

Input File Setup

Input File: vmc.inp

%module general
    title           'Test LiF'
    basis            BASISGRID  # Grid basis
    mode            'vmc_one_mpi'
    iforce_analy     1          # Enable force analysis
    iperiodic        1          # Enable periodic boundary conditions
    np_coul          2          # Ewald summation parameter
    cutg             3.84       # G-vector cutoff
    n_images         2          # Periodic images
%endmodule

load lattice         box.txt    # Define unit cell
load molecule        geo        # Atomic positions

# ... standard loads ...

Key Keywords

  • iperiodic 1: Activates periodic handling in the Hamiltonian.
  • load lattice: Reads the simulation cell vectors.
  • iforce_analy 1: Calculation of Hellmann-Feynman (and Pulay) forces.

Resources: Periodic Force Test