fermiq / airebo-m

Source files for implementation of the AIREBO-M interatomic potential

IMPORTANT NOTE:

AIREBO-M is now part of the main LAMMPS distribution, as part of the airebo pair_style. I encourage anyone who wants to use AIREBO-M in LAMMPS to use this version, as it is maintained and updated with all the most recent LAMMPS updates and bugfixes. I plan to maintain this repository as reliable location for airebo-m parameter files.

-Thomas C. O'Connor (3.21.2016)

AIREBO-M

This repository contains source files for the LAMMPS implementation of the AIREBO-M reactive bond order potential for hydrocarbons, described in O'Connor et al., J. Chem. Phys. 142, 024903 (2015).

AIREBO-M is a modified version of the the AIREBO potential described in Stuart et al., J. Chem. Phys. 112, 6472 (2000). AIREBO-M replaces the Lennard-Jones potentials of AIREBO's van der Waal's interactions with Morse potentials. The Morse potentials are parameterized by high-quality quantum chemistry (MP2) calculations. The Morse potentials, which do not diverge as particle density increases, allow AIREBO-M to retain accuracy to much higher pressures than AIREBO (up to 40 GPa for Polyethylene).

##Compiling With LAMMPS

Compiling AIREBO-M with LAMMPS is simple if you have already successfully compiled the default LAMMPS build which contains AIREBO. The repository contains the following files:

1. pair_airebo_morse.cpp
2. pair_airebo_morse.h
3. CH.airebo-m

Just place the .cpp and .h files in the lammps[version]/src/ directory and compile LAMMPS. The file CH.airebo-m is the potential paramter file accessed by the pair_coeff command in a LAMMPS script.

##Usage in LAMMPS

Using AIREBO-M in LAMMPS is identical to using AIREBO, with one important exception. AIREBO-M takes an additional 3rd flag in the pair_style command:

pair_style        style cutoff LJ_flag TORSION_flag REBO_flag

• cutoff = Long range cutoff of Morse potentials
• LJ_flag = switches on/off the Morse potentials
• TORSION_flag = switches on/off the AIREBO torsion energies
• REBO_flag = switches on/off the covalent REBO2 energies

A typical implementation in a LAMMPS script would be:

pair_style        airebo_morse 3.0 1 1 1
pair_coeff        * * CH.airebo-m C H

Note: The AIREBO-M Morse potentials were parameterized using a cutoff of 3.0 (sigma). Modifying this cutoff may effect simulation accuracy.

The REBO_flag is included so that the Morse potentials can be used with other implementations of the REBO2 covalent interactions. For example, one can use the REBO_flag to disable the REBO2 term of AIREBO-M, and use pair_style hybrid/overlay replace it with the bond-screening version (REBO2Scr) of Pastewka et al., Phys. Rev. B 78, 161402 (2008). We've recently used this hybrid technique to produce good quality results for polyethylene crystals in ACS Macro Lett., 2016, 5, pp 263–267

pair_style        hybrid/overlay atomistica Rebo2Scr airebo_morse 3.0 1 1 0
pair_coeff        * * atomistica C H
pair_coeff        * * airebo_morse CH.airebo-m C H

(REBO2Scr can be implemented in LAMMPS via the Atomistica repository.)

##Compatibility AIREBO-M has been succesfully compiled in lammps-15Jan16.