1. Basic Ground State Energy with CPU build

This example covers running AFQMC for a generic input Hamiltonian to obtain the ground state energy. It assumes that you already have an HDF5 file containing a Hamiltonian and trial wavefunction. If not, see the examples in Setting Up AFQMC.

Here, it is assumed that a Hamiltonian and a trial wavefunction are both saved in an HDF5 file called afqmc.h5. SAFIRE uses an input file in .json format to set parameters in calculations. The input file is explained in detail in Input file, but a minimal example is shown here.

{
  "afqmc": {
    "project": {
      "id": "qmc",
      "series": 0
    },
    "execute": {
      "walker_set": {
        "walker_type": "COLLINEAR"
      },
      "wavefunction": {
        "filename": "afqmc.h5"
      },
      "timestep": 0.01,
      "steps": 10000,
      "n_walkers_per_mpi_task": 60,
      "accumlate_interval": 2,
      "population_control_interval": 2,
      "seed": 42
    }
  }
}

Note that all intervals are expressed in units of “steps”.

A CPU-only build of SAFIRE can be invoked on rusty using the following runscript,

#!/bin/bash -l
#SBATCH -J afqmc
#SBATCH --partition=ccq
#SBATCH --constraint=ib
#! Number of MPI ranks (= tasks for Slurm)
#SBATCH --ntasks=160
#SBATCH --time=0:30:00

export AFQMC_PATH=/path/to/your/afqmc/build

module purge
source $AFQMC_PATH/env.bash

# Launch MPI code...
srun --cpu-bind=cores $AFQMC_PATH/bin/safire --filenames afqmc.json &> afqmc.out

If the Hamiltonian and trial wavefunction file from Rectangular Hubbard Model (called “afqmc.h5”) is used with the input file above, then we will see output similar to this (perhaps with differences in the timing)

See Analyzing Scalar Data for an example of analyzing this output.