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#36289 - 03/13/17 06:39 AM QM/MM energy minimzation - upticks in the energy
simond Offline
Forum Member

Registered: 01/13/17
Posts: 6
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:

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?

Gnuplot+%28window+id+_+0%29+2017-03-13+11.25.10.png (146 downloads)

Edited by simond (03/13/17 06:40 AM)

#36292 - 03/14/17 02:24 PM Re: QM/MM energy minimzation - upticks in the energy [Re: simond]
rmv Offline

Forum Member

Registered: 09/17/03
Posts: 8379
Loc: 39 03 48 N, 77 06 54 W
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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