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QMMM Interaction Energy
#37779 12/09/19 10:56 PM
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bnumn Offline OP
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I am trying to calculate the interaction energy between the QM region and the surrounding solvent in a QM/MM system. The system consists only of a simple solvated molecule which is in the QM region.

Based on previous threads, I have ensured that there isn't any images or ewald and all the relevant non-bonded parameters have been declared (CODES, nbond and hbond). I called the 'update' command, followed by the 'energy' command, followed by the 'interaction' command.

The energy command worked as intended, but the interaction command returned 0.000 as the interaction energy. What am I missing here?



ENER ENR: Eval# ENERgy Delta-E GRMS
ENER EXTERN: VDWaals ELEC HBONds ASP USER
ENER QUANTUM: QMELec QMVDw
---------- --------- --------- --------- --------- ---------
ENER> 0 -36478.09702 0.00000 12.66135
ENER EXTERN> 4129.39894 -40137.83922 0.00000 0.00000 0.00000
ENER QUANTM> -455.91736 -13.73939
---------- --------- --------- --------- --------- ---------


INTE ENR: Eval# ENERgy Delta-E GRMS
---------- --------- --------- --------- --------- ---------
INTE> 1 0.00000 -36478.25474 0.00000
---------- --------- --------- --------- --------- ---------

Re: QMMM Interaction Energy
bnumn #37782 12/10/19 09:01 PM
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rmv Online Content
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You wish to provide some more detail, such as the CHARMM version and which QM package and version is being used.


Rick Venable
computational chemist

Re: QMMM Interaction Energy
bnumn #37785 12/12/19 08:26 PM
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bnumn Offline OP
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Thanks for the reply.

The version that I am using is C42b1. I have tried the same procedure with the quantum, the squantum and the mndo97 package to the same effect. I believe the issue is related to the non-bonded interaction with the QM region. Using the same selection, the MM INTE is correct, whereas the QM/MM INTE shows that there wasn't any Nonbond interactions selected:

MM:
SELRPN> 14 atoms have been selected out of 12489
SELRPN> 3 atoms have been selected out of 12489
INTER: Normal Atom Nonbondselected 42 from a total of 5167686
INTE ENR: Eval# ENERgy Delta-E GRMS
INTE EXTERN: VDWaals ELEC HBONds ASP USER
---------- --------- --------- --------- --------- ---------
INTE> 1 -14.42337 311624.14406 0.21122
INTE EXTERN> -0.09128 -14.33209 0.00000 0.00000 0.00000
---------- --------- --------- --------- --------- ---------

QM/MM:

SELRPN> 14 atoms have been selected out of 12489
SELRPN> 3 atoms have been selected out of 12489
INTER: Normal Atom Nonbondselected 0 from a total of 5151575
INTE ENR: Eval# ENERgy Delta-E GRMS
---------- --------- --------- --------- --------- ---------
INTE> 1 0.00000 -35696.47182 0.00000
---------- --------- --------- --------- --------- ---------



For the non-bonded parameters, I've tried a wide variety including the ones suggested by admins for this application which are:

update cutnb 13.0 ctofnb 12.0 ctonnb 10. fshift vfswitch
and
update cutnb 12.0 ctofnb 12.0 fshift vshift cdie

The QM/MM command used is:

quantum group sele @selection end remove charge -1 AM1 norder 6


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