emarinri / hfcs-fffit

Force field fitting for HFCs with fffit package

hfcs-fffit

hfcs-fffit is a repository used for a case study of our machine learning directed force field optimization workflow outlined in this preprint. Here we use the procedure to generate force fields for two hydrofluorocarbons (HFCs), HFC-32 and HFC-125.

Citation

This work has been submitted for review. In the meantime, you may cite the preprint as:

BJ Befort, RS DeFever, GM Tow, AW Dowling, and EJ Maginn. Machine learning
directed optimization of classical molecular modeling force fields. arXiv
(2021), https://arxiv.org/abs/2103.03208

Available Data

HFC Parameter Sets

The non-dominated and "top four" parameter sets for each HFC are provided under hfcs-fffit/analysis/csv/. The non-dominated sets are found in r32-pareto.csv and r125-pareto.csv, and the "top four" sets are found in r32-final-4.csv and r125-final-4.csv. The parameter values in the csv files are normalized between 0 and 1 based upon the parameter bounds for each atom type (see manuscript, or hfcs-fffit/analysis/utils/r32.py and hfcs-fffit/analysis/utils/r125.py for definitions of the upper and lower parameter bounds).

Molecular Simulations Inputs

All molecular simulations were performed under hfcs-fffit/runs. Each iteration was managed with signac-flow. Inside of each directory in runs, you will find all the necessary files to run the simulations. Note that you may not get the exact same simulation results due to differences in software versions, random seeds, etc. Nonetheless, all of the results from our molecular simulations are saved under hfcs-fffit/analysis/csv/rXX-YY-iterZZ-results.csv, where XX is the molecule, YY is the stage (liquid density or VLE), and ZZ is the iteration number.

Surrogate Modeling Analysis

All of the scripts for the surrogate modeling are provided in hfcs-fffit/analysis, following the same naming structure as the csv files.

Figures

All scripts required to generate the primary figures in the manuscript are reported under hfcs-fffit/analysis/final-figs and the associated PDF files are located under hfcs-fffit/analysis/final-figs/pdfs.

Using This Package

Installation

This package has a number of requirements that can be installed in different ways. We recommend using a conda environment to manage most of the installation and dependencies. However, some items will need to be installed from source or pip.

We recommend starting with a fresh conda environment, then installing the packages listed under requirements-pip.txt with pip, then installing the packages listed under requirements-conda.txt with conda, and finally installing a few items from source requirements-other.txt. We recommend python3.7 and taking packages from conda-forge.

Running the simulations will also require an installation of GROMACS. This can be installed separately (see installation instructions here).

WARNING: Cloning the hfcs-fffit repository will take some time and ~1.5 GB of disk space since it contains the Latin hypercube that have ~1e6 parameter sets each.

An example of the procedure is provided below:

# First clone hfcs-fffit and install pip/conda available dependencies
# with a new conda environment named hfcs-fffit
git clone [email protected]:dowlinglab/hfcs-fffit.git
cd hfcs-fffit/
conda create --name hfcs-fffit python=3.7 -c conda-forge
conda activate hfcs-fffit
python3 -m pip install -r requirements-pip.txt
conda install --file requirements-conda.txt -c conda-forge
cd ../

# Now clone and install  other dependencies
git clone [email protected]:dowlinglab/fffit.git
# Checkout the v0.1 release of fffit and install
cd fffit/
git checkout tags/v0.1
pip install .
cd ../
# Checkout the v0.1 release of block average and install
git clone [email protected]:rsdefever/block_average.git
cd block_average/
git checkout tags/v0.1
pip install .
cd ../

HFC-32 Liquid Density Optimization

NOTE: We use signac and signac flow (https://signac.io/) to manage the setup and execution of the molecular simulations. These instructions assume a working knowledge of that software.

The first iteration of the liquid density simulations were performed under the hfcs-fffit/runs/r32-density-iter1/. A Latin hypercube with 200 parameter sets exists under hfcs-fffit/runs/r32-density-iter1/data/lh_samples_200_r32.txt. The signac workspace is created by hfcs-fffit/runs/r32-density-iter1/init.py.

cd hfcs-fffit/runs/r32-density-iter1/
python init.py

The thermodynamic conditions for the simulations and the bounds for each parameter (LJ sigma and epsilon for C, F, and H) are defined inside init.py.

The simulation workflow is defined in hfcs-fffit/runs/r32-density-iter1/project.py. The flow operations defined therein create the simulation input files, perform the simulations, and run the analysis (calculating the average density). In order to run these flow operations on a cluster with a job scheduler, it will be necessary to edit the files under hfcs-fffit/runs/r32-density-iter1/templates/ to be compatible with your cluster. The signac documentation contains the necessary details.

Once the first iteration of simulations have completed (i.e., all the flow operations are done), you can perform analysis. The necessary files are located under hfcs-fffit/runs/analysis and hfcs-fffit/runs/analysis/r32-density-iter1. The first step is to extract the results from your signac project into a CSV file so they can be stored and accessed more easily in the future. This step is performed by extract_r32_density.py. The script requires the iteration number as a command line argument.

WARNING: Running this script will overwrite your local copy of our simulation results (stored as CSV files) with the results from your simulations.

To extract the results for iteration 1 run the following:

cd hfcs-fffit/analysis/
python extract_r32_density.py 1

The CSV file with the results is saved under hfcs-fffit/analysis/csv/rXX-YY-iterZZ-results.csv where XX is the molecule, YY is the stage (liquid density or VLE), and ZZ is the iteration number.

The analysis is performed within a separate directory for each iteration. For example, for the first iteration, it is performed under hfcs-fffit/analysis/r32-density-iter1. The script id-new-samples.py loads the results from the CSV file, fits the SVM classifier and GP surrogate models, loads the Latin hypercube with 1e6 prospective parameter sets, and identifies the 200 new parameter sets to use for molecular simulations in iteration 2. These parameter sets are saved to a CSV file: hfcs-fffit/analysis/csv/r32-density-iter2-params.csv.

The second iteration of the liquid density simulations were performed under the hfcs-fffit/runs/r32-density-iter2/. The procedure is the same as for iteration 1, but this time the force field parameters are taken from: hfcs-fffit/analysis/csv/r32-density-iter2-params.csv. The procedure for analysis is likewise analogous to iteration 1, however, note that in training the surrogate models, hfcs-fffit/runs/analysis/r32-density-iter2/id-new-samples.py now uses the simulation results from both iterations 1 and 2.

HFC-32 VLE Optimization

The optimization for the vapor-liquid equilibrium iterations is very similar. The final (iteration 4) liquid density analysis saves the parameters as hfcs-fffit/analysis/csv/r32-vle-iter1-params.csv. The first VLE iteration begins with these parameters. Once again, the simulations are performed under: hfcs-fffit/runs/r32-vle-iter1. The init.py is used to set up the signac workspace, and project.py defines the simulation workflow (create the inputs, perform the molecular simulations, and run the analysis). The results are extracted into the CSV file with hfcs-fffit/analysis/extract_r32_vle.py. Once again the iteration number is a command line argument, and the results are saved to a CSV file hfcs-fffit/analysis/csv/r32-vle-iter1-results.csv.

Each VLE iteration has a folder with the analysis scripts (e.g., hfcs-fffit/analysis/r32-vle-iter1). The analysis.py and evaluate-gps.py perform basic analysis and create figures evaluating the performance of the GP models. The id-new-samples.py loads a Latin hypercube with 1e6 prospective parameter sets, and identifies the top-performing parameter sets which will be evaluated with molecular simulations during the subsequent iteration. For example, the parameter sets to be used for the second VLE iteration are saved to hfcs-fffit/analysis/csv/r32-vle-iter2-params.csv. Each subsequent VLE iteration is performed in the same manner.

Credits

This work was supported by the National Science Foundation under grant NSF Award Number OAC-1835630 and NSF Award Number CBET-1917474. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.