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QM/MM energy minimzation - upticks in the energy
#36289 03/13/17 10:39 AM
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simond Offline OP
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I'm performing a QM/MM energy minimization with ABNR in c38b2 with the CHARMM/Turbomole interface.
The system is a solvated protein/NA complex where I have fixed everything except a sphere within 15A of an active site residue.
I'm using the CHARMM36 parameters.
The calculation is with:
Code:
FASTER OFF
SKIP NONE

ELEC     VDW      ATOMs    CDIElec  SWITch   VATOm    VSWItch
     BYGRoup  NOEXtnd  NOEWald
 CUTNB  =160.000 CTEXNB =999.000 CTONNB =100.000 CTOFNB =120.000
 CGONNB =  0.000 CGOFNB = 10.000
 WMIN   =  1.500 WRNMXD =  0.500 E14FAC =  1.000 EPS    =  1.000
 NBXMOD =      5


If I do the energy minimization I observe, that there are certain upticks in the energy(see image, plotted are the value directly behind the "MINI>"). The total trend however is to a lower energy. What could be the reason for these upticks?


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Last edited by simond; 03/13/17 10:40 AM.
Re: QM/MM energy minimzation - upticks in the energy
simond #36292 03/14/17 06:24 PM
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rmv Online Content
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I don't think it's that unusual for ABNR to report a higher energy for a particular step during an extended minimization.

Have you assessed the impact of the size of constraint sphere?

Note that there is a QM/MM forum for issues involving external QM programs interfaced to CHARMM.


Rick Venable
computational chemist


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