Execution with Quickrun#

The planning and preparation of a campaign of alchemical simulations using openfe is intended to be achievable on a local workstation in a matter of minutes. The execution of these simulations however requires a large amount of computational power, and beyond running single calculations locally, is intended to be distributed across a HPC environment. Doing this requires storing and sending the details of the simulation from the local workstation to a HPC environment, which can be done via the Transformation.to_json() function which creates a saved JSON version of the data. These serialized JSON files are the currency of executing a campaign of simulations and contain all the information required to execute a single simulation.

To read the Transformation information and execute the simulation, the command line interface provides the openfe quickrun command, the full details of which are given in the CLI reference section. Briefly, this command takes in the Transformation information represented as JSON, then executes a simulation according to those specifications. For example, the following command executes a simulation defined by transformation.json and produces a results file named results.json.

openfe quickrun transformation.json -o results.json

Executing within a job submission script#

You may need to submit computational jobs to a queueing engine, such as Slurm. The openfe quickrun command can be used within a submission script as follows:

#!/bin/bash

#SBATCH --job-name="openfe job"
#SBATCH --mem-per-cpu=2G

# activate an appropriate conda environment, or any "module load" commands required to
conda activate openfe_env

openfe quickrun transformation.json -o results.json

Parallel execution of repeats with Quickrun#

Serial execution of multiple repeats of a transformation can be inefficient when simulation times are long. Higher throughput can be achieved with parallel execution by running one repeat per HPC job. Most protocols are set up to run three repeats in serial by default, but this can be changed by either:

  1. Defining the protocol setting protocol_repeats - see the protocol configuration guide for more details.

  2. Using the openfe plan-rhfe-network (or plan-rbfe-network) command line flag --n-protocol-repeats.

Each transformation can then be executed multiple times via the openfe quickrun command to produce a set of repeats. However, you must use unique results files for each repeat to ensure they don’t overwrite each other. We recommend using folders named results_x where x is 0-2 to store the repeated calculations as our openfe gather command also supports this file structure.

Below is an example of a simple script that will create and submit a separate job script (\*.job named file) for every alchemical transformation (for the simplest SLURM use case) in a network running each repeat in parallel and writing the results to a unique folder:

for file in network_setup/transformations/*.json; do
  relpath="${file:30}"  # strip off "network_setup/"
  dirpath=${relpath%.*}  # strip off final ".json"
  jobpath="network_setup/transformations/${dirpath}.job"
  if [ -f "${jobpath}" ]; then
    echo "${jobpath} already exists"
    exit 1
  fi
  for repeat in {0..2}; do
    cmd="openfe quickrun ${file} -o results_${repeat}/${relpath} -d results_${repeat}/${dirpath} --n-protocol-repeats 1"
    echo -e "#!/usr/bin/env bash\n${cmd}" > "${jobpath}"
    sbatch "${jobpath}"
  done
done

This should result in the following file structure after execution:

results_parallel/
├── results_0
│   ├── rbfe_lig_ejm_31_complex_lig_ejm_42_complex
│   │   └── shared_RelativeHybridTopologyProtocolUnit-79c279f04ec84218b7935bc0447539a9_attempt_0
│   │       ├── checkpoint.nc
│   │       ├── simulation.nc
│   ├── rbfe_lig_ejm_31_complex_lig_ejm_42_complex.json
├── results_1
│   ├── rbfe_lig_ejm_31_complex_lig_ejm_42_complex
│   │   └── shared_RelativeHybridTopologyProtocolUnit-a3cef34132aa4e9cbb824fcbcd043b0e_attempt_0
│   │       ├── checkpoint.nc
│   │       ├── simulation.nc
│   ├── rbfe_lig_ejm_31_complex_lig_ejm_42_complex.json
└── results_2
    ├── rbfe_lig_ejm_31_complex_lig_ejm_42_complex
    │   └── shared_RelativeHybridTopologyProtocolUnit-abb2b104151c45fc8b0993fa0a7ee0af_attempt_0
    │       ├── checkpoint.nc
    │       ├── simulation.nc
    └── rbfe_lig_ejm_31_complex_lig_ejm_42_complex.json

The results of which can be gathered from the CLI using the openfe gather command, in this case you should direct it to the root directory which includes the repeat results and it will automatically collate the information

openfe gather results_parallel

Optimizing GPU performance with NVIDIA MPS#

You can further optimize execution of openfe quickrun using NVIDIA’s Multi-Process Service (MPS). See NVIDIA’s documentation on MPS for OpenFE free energy calculations for details.

See Also#

For details on inspecting these results, refer to Results Gathering.