LAMMPS and DREIDING hydrogen bonding potential

Dear Steve and Tod

I am running some calculations to output energy values for a same system with and without DREIDING hydrogen bonding potential (henceforth denoted as hbp). When hbp is ON, lammps outputs total potential energy to be less than that when hbp OFF by 140 kcal/mol. As expected this difference comes from the difference in pair energy in the two cases. In pair energy, elong is same, whereas surprisingly ecoul is less by 111 kcal/mol and evdw less by 29 kcal/mol in case of hbp ON as compared to OFF case. Since DREIDING 1990 article clearly says that all electrostatic and VdW interactions are to be included in hbp ON case, I wonder why there is such a difference with respect to these two energy values. I initially thought that difference in epair is due to difference in hydrogen bonding energy, however, when I outputted hydrogen bonding energy it comes down to meager 0.042842881 kcal/mol. I used the same syntax as mentioned on lammps page:

compute hb all pair hbond/dreiding/morse
variable n_hbond equal c_hb[1] #number hbonds
variable E_hbond equal c_hb[2] #hbond energy

thermo_style custom step cpu press temp pe ke etotal enthalpy evdwl v_E_hbond v_n_hbond ecoul epair ebond eangle edihed eimp emol elong etail vol lx ly lz

Could you clarify please? Thank you very much.


Sorry! I should have checked the patches before sending following email. There is a patch submitted in Oct 2011, that I need to apply.