Param.qeq file

Dear Lammps Users,

It would be so appreciated if you could explain how obtain the parameters in param file in fix qeq/reax. One can get the second and third columns of this file from DFT calculations using chi=1/2(IP+EA) and eta=IP-EA equations, but what about valence orbital exponent gamma?
Thank you very much in advance,

Department of Physics,
Amirkabir University.

They should be part of the ReaxFF parameter set/file. The recommended way is to use the “reaxff” keyword which will then extract the settings from the pair style. The option to use an explicit file is mostly to allow experts to experiment with changing parameters and to support a different implementation of ReaxFF in LAMMPS that has since been obsoleted.

As mentioned, the fix QEQ1 all qeq/reax 1 0.0 10.0 1e-6 reaxff command automatically extracts values from the force-field file.

If you want to use the fix QEQ1 all qeq/reaxff 1 0.0 10.0 1.0e-6 param.qeq command, you will need to provide a file called param.qeq and carefully specify the values for itype chi eta gamma . These values can be found in the force-field file :

4 ! Nr of atoms; cov.r; valency;a.m;Rvdw;Evdw;**gammaEEM**;cov.r2;# alfa;gammavdW;valency;Eunder;Eover;**chiEEM**;**etaEEM**;n.u. cov r3;Elp;Heat inc.;n.u.;n.u.;n.u.;n.u.

Note that the value for eta in the file is defined as twice the eta value used in the ReaxFF file.

Thank you very much for your quick response.

Thank you very much for your help.