diff --git a/tools/tabulate/pair_bi_tabulate.py b/tools/tabulate/pair_bi_tabulate.py new file mode 100755 index 0000000000..910bedf64e --- /dev/null +++ b/tools/tabulate/pair_bi_tabulate.py @@ -0,0 +1,117 @@ +#!/usr/bin/env python3 + +from tabulate import PairTabulate +import sys +import argparse +import numpy as np +from scipy.signal import savgol_filter +from scipy.optimize import curve_fit + +""" + This script gives an example on how to make tabulated forces from radial + distribution function using tabulate.py. + Required: python3, numpy, scipy. + BI stands for Boltzmann Inversion. +""" +############################################################################### + + +class BI(PairTabulate): + def __init__(self, units=None, comment=None, T=1): + super(PairTabulate, self).__init__("pair", self.energy, units, comment) + self.parser.add_argument( + "--eshift", + "-e", + dest="eshift", + default=False, + action="store_true", + help="Shift potential energy to be zero at outer cutoff", + ) + self.parser.add_argument( + "--rdffile", default="rdf.dat", help="Rdf file to be read." + ) + try: + self.args = self.parser.parse_args() + except argparse.ArgumentError: + sys.exit() + + kb = 1 + # Add more kb units if you need + if units == "si": + kb = 1.380649e-23 # J/K + elif units == "metal": + kb = 8.617333e-5 # eV/K + elif units == "real": + kb = 1.987204e-3 # kcal/mol/K + else: + sys.stdout.write("WARNING: Unknown or lj units, using kb=1\n") + self.kbT = kb * T + self.r, self.e, self.f = self.read_rdf(self.args.rdffile) + + # This function assumes LAMMPS format for rdf with a single entry + def read_rdf(self, rdffile): + data = np.loadtxt(rdffile, skiprows=4) + r = data[:, 1] + g = data[:, 2] + + # savgol_filter is an example of smoothing. + # Other filters/functions can be used. + g = savgol_filter(g, 10, 5) + return self.inversion(r, g) + + def inversion(self, r, g): + r = r + e = -self.kbT * np.log(g) + e = self.complete_exponential(r, e) + f = -np.gradient(e, r) + return r, e, f + + def complete_exponential(self, r, e): + r_temp = r[e != np.inf] + e_temp = e[e != np.inf] + + # Optimising the parameter for a function for derivation + # to be continuous. + # Here a gaussian function, can be anything relevant defined in func. + popt, pcov = curve_fit(self.func, r_temp[:2], e_temp[:2]) + for i, _ in enumerate(e): + if e[i] == np.inf: + e[i] = self.func(r[i], *popt) + return e + + def func(self, x, K, s): + return K * np.exp(-0.5 * (x / s) ** 2) / (s * np.sqrt(2 * np.pi)) + + def energy(self, x): + e = self.e + r = self.r + # Force estimation at minimum distance. + # Should not be that useful + f0 = (e[1] - e[0]) / (r[1] - r[0]) + + minr = min(r) + maxr = max(r) + # Note that you might want OOB to return an error. + if x >= maxr: + return 0 + if x < minr: + dx = minr - x + return -f0 * dx + else: + # Linear interpolation between points. + for i, ri in enumerate(r): + if r[i] < x: + r1, e1 = r[i], e[i] + r2, e2 = r[i + 1], e[i + 1] + dr12 = r2 - r1 + dr = x - r1 + de = (e2 - e1) / (r2 - r1) + return e1 + (de * dr / dr12) + + +############################################################################### + + +if __name__ == "__main__": + ptable = BI() + ptable.run("BI")