AMBER Archive (2009)

Subject: Re: [AMBER] How to get total energy of a system from QM/MM

From: steinbrt_at_rci.rutgers.edu
Date: Wed Dec 02 2009 - 03:53:03 CST

Hi,

>                     FINAL RESULTS
>
>    NSTEP       ENERGY          RMS            GMAX         NAME    NUMBER
>    5000      -8.3914E+03     1.4084E+01     3.7616E+01     O         794
[...]
>   PM3ESCF =    -1020.4525

The QM energy is part of the overall total energy in Amber. So the -8391
kcal/mol total energy above includes E(QM) as well as E(MM). Therefore the
Total energy Amber reports is the true total energy for your QM/MM system,
but as always given with respect to an arbitrary zero. Interpreting this
energy (e.g. for conformational stability) is very tricky, since there is
no entropy component in it.

Kind Regards

Dr. Thomas Steinbrecher
BioMaps Institute
Rutgers University
610 Taylor Rd.
Piscataway, NJ 08854

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