aehogan / ffit

Quick and dirty code to fit emperical forcefield nonbonded parameters to ab initio single points.

ffit

Quick and dirty code to fit emperical forcefield nonbonded parameters to ab initio single points.

Building

git clone https://github.com/aehogan/ffit.git
cd ffit
mkdir build
cd build
cmake ..
make

Testing

cd ffit/examples
../build/ffit he.inp

Data files

See examples/co2.data or examples/he.data for the format of ab initio input data. Briefly, the data files are modified XYZ format files with the ab initio energy in K/kB on the comment line and a molecule id number added before the XYZ data and an atomic charge added after.

Input commands

• Lines starting with ! or # are treated as comments
• steps [int]
  • number of fitting steps, can be zero to only print out information of the current fit
• output_freq [int]
  • after how many steps to print fitting information
• max_energy [float]
  • the energy scaling parameter to start reducing the important of very repulsive configurations
• data_file [str]
  • filename for an ab initio data file
• es [on|off]
  • permanent electrostatics on / off
• pol [on|off]
  • induced dipole electrostatics on / off
• lj [on|off]
  • Lennard-Jones potential on / off
• phahst [on|off]
  • modified tang toennies (exponential 6-8-10) on / off
• type_map [str] [int]
  • atom name to atom id
• lj_sig [int] [float]
  • atom id and initial Lennard-Jones sigma (or exponential rho) in angstrom
• lj_eps [int] [float]
  • atom id and initial Lennard-Jones epsilon (or exponential beta) in K/kB (or angstrom^-1)
• c6 [int] [float]
  • atom id and initial c6 in a.u.
• c8 [int] [float]
  • atom id and initial c8 in a.u.
• c10 [int] [float]
  • atom id and initial c10 in a.u.
• alpha [int] [float]
  • atom id and initial polarizability in angstrom^3