Dear Jon,
To the best of my knowledge the potential energy is the sum of all
energies (E_QM + E_MM + E_QM/MM). The quantum energy (actually I do not
see it in my output) for electrostatic embedding includes E_QM +
E_QM/MM(el.stat.). I.e. E_QM/MM(VDW) you have to extract from the edr
file. You should have two different energy groups, one defining the QM,
and the other one defining the remaining system. I.e. you can extract
E_QM/MM(VDW) from the sum of LJ-SR:notQM-QM and LJ-14:notQM-QM.
Importantly, if you want to analyze the QM_part of the energy, you
should (i) either calculate E_QM without the point charges again, or
(ii) add E_QM/MM(VDW) to the printed quantum energy (i.e. calculate E_QM
+ E_QM/MM), since the electrostatic QM/MM contribution is included in
the quantum energy for electrostatic embedding, and it is highly
dependent on the respective VDW contribution.
Hope that helps,
Christoph Riplinger
On 11/25/2011 11:08 AM, Jon Mujika wrote:
Dear gmx users,
I am performing some QM/MM optimizations using the ORCA interface in
order to compare the energies of different structures of the same
system. However, I have some questions related with the energy terms.
In the output file the "potential" and "Quantum Ener." terms are
printed out. The question is: does the Potential term include the QM
energy? That is, is the "potential" energy the total QM/MM energy, or
only the MM part of the total energy? On the other hand, since I am
using the electronic embedding approach (QMMMscheme=normal in the .mdp
file), I assume that the QM/MM electrostatic energy is included in the
QM term. Is that correct? And what about the QM/MM van der Waals
energy?
I ask so because I try to calculate the potential energy from the
different terms provided in the output, but I can't reproduce the
potential energy.
Thanks for you help
Jon
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