CHARMM Development Project Forums User Discussion & Questions Energy terms, Constraints, Restraints, and Solvation High frequency correction energy

Hi All,

Could somebody please tell me what exactly "high frequency correction energy" means? I mean the EHFC term in the energy output. I am trying to run a simulation uisng HARMonic constraint, but the EHFC, and so the total energy, keeps decreasing. Any help would be appreciated.

EHFC is a modest correction to energy due to high frequency motions; it's more likely to be a symptom, rather than the cause of problems from a simulation with harmonic restraints. The restraints are the more likely cause of instability, and probably need to be changed.

Hi Eric,

Thank you so much for replying.
Do you mean that whenever this term is large, something is wrong (even if it is constant)?
Thanks again

Probably, although it's hard to generalize out of context. It should be a small fraction of the potential, and smaller than e.g. the DIHE term.

Are you using the DYNA VV2 integrator with thermostats (TPCONTROL)? In that case, the EHFC terms contains more than the usual: It also has the energy content of the heat bath -- which may decrease steadily if you put external couplings such as HARM.

Look at this post for more information.

Guillaume

Hi Guillaume,
I am using VVER with NOSE temperature control. Does this make any difference?

Perhaps, and you should consider using some other method for T control. The VVER integrator is not very good, but features are hardly ever removed from CHARMM.

Good, I was wondering about this term. So, how HFCTote and TOTEner are related? I see that in my log file HFCTote is not a small number, in fact it is as great as TOTEner.

HFCT is the corrected total energy, not the correction, thus HFCT and TOTE are very similar; HFCT will be more (slightly more) stable over time.