threebodyparah2

The threebodyparah2 program will use the RKHS method with the grid of aug-cc-pVTZ data points (with empirical adjustments) to calculate the three-body correction energy to the parahydrogen triplet. Only the isotropic term in the potential expansion is used. The program accepts as parameters the three side lengths of the triangle (in Angstroms), and returns the three-body correction energy in cm^{-1}.

The input file takes the form of three columns of whitespace-delimited floating point numbers. Each line corresponds to a different triangular configuration for the three hydrogen molecules. The order of the three pair distances isn't important (i.e. the labels {1, 2, 3} for the molecules is arbitrary); the distances are sorted within the program.

The 1st column represents the pair distances between molecules 1 and 2. The 2nd column represents the pair distances between molecules 2 and 3. The 3rd column represents the pair distances between molecules 1 and 3.

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Installation:

Part 1: create the threebodyparah2 PES executable

cd src
make                                            
cd ..

Part 2: create the threebodypes.kernel file in RKHS/kernels

cd RKHS
make
python generate_kernel.py                       
cd ..

Part 3: test the executable

cp kernels/threebodypes.kernel test
cp src/threebodyparah2 test
cd test

test using equilateral triangles:

./threebodyparah2 threebodypes.kernel tsl_equilateral.dat

test using random triangles:

./threebodyparah2 threebodypes.kernel tsl_random.dat

several examples of curves using the three-body potential:

python plot_examples.py

uncomment lines at the bottom of the script for different plots more instructions are inside the plot_examples.py file

Part 4 (OPTIONAL): create the threebodypes.csv file from the AVTZ data

this step assumes:

• the threebodyparah2 executable in Part 1 has been created
• make has already been run in Part 2

descriptions of the adjustments are given at the top of the files:

• make_smodAVTZ_csvfile.py
• make_RsmodAVTZ_csvfile.py
• make_threebodypes_csvfile.py

the resulting threebodypes.csv file is saved in the makecsv directory, not the csvfiles directory:

cd makecsv
python makecsv.py

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TESTED COMPILERS:

• GNU Fortran, version 9.3.0
• g++, version 9.3.0

PYTHON REQUIREMENTS

• Python 3.6.7 or above
• numpy
• scipy

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NOTES:

1. The threebodypes.kernel file must be in the same directory as the threebodyparah2 executable.
2. The program does not check if the triangles inserted are 'impossible', i.e. if you include a "triangle" where one side length is greater than the sum of the other two, a junk value comes out, or a segmentation fault occurs.