Previous Thread
Next Thread
Print Thread
QM/MM energy minimzation - upticks in the energy
#36289 03/13/17 10:39 AM
Joined: Jan 2017
Posts: 6
simond Offline OP
Forum Member
OP Offline
Forum Member
Joined: Jan 2017
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?

Attached Files
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
Joined: Sep 2003
Posts: 8,450
rmv Online Content
Forum Member
Online Content
Forum Member
Joined: Sep 2003
Posts: 8,450
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

Moderated by  BRBrooks, John Legato 

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.4
(Release build 20200307)
Responsive Width:

PHP: 5.6.33-0+deb8u1 Page Time: 0.008s Queries: 19 (0.004s) Memory: 0.8931 MB (Peak: 0.9619 MB) Data Comp: Off Server Time: 2020-06-03 19:42:47 UTC
Valid HTML 5 and Valid CSS