Dear Amber developers,
I was trying to get the mulliken charges for the DFTB/MM calculation. In the beginning, I was using sander to do the DFTB/MM calculation, but it seems that sander does not support to print the mulliken charges information, so I turned to sqm. According to the manual, the code of sqm is extracted from sander, so I assume that the result of energy should also match with sander (as long as the settings are the same), with the ability to print the mulliken charges. However, I have tried to keep the settings same and do calculation for the same frames (capped alanine in solution with no periodicity), but the results do not match. I was wondering if this is normal, or something different need to be set for sqm.
My qmmm settings for sander look like:
&cntrl
imin=5,
ntx=5,
irest=1,
cut=9999.0,
ntb=0,
ntwx=1,
ntwf=1,
ioutfm=0,
ifqnt=1
/
&qmmm
qmmask=':1-3',
qm_theory='DFTB',
dftb_disper=1,
qmcharge=0,
spin=1,
qmshake=0,
qm_ewald=0, qm_pme=0,
/
I have extracted the coordinates, the MM charges (in a.u. or e), and my input for sqm looks like:
Run semi-empirical minimization
&qmmm
qm_theory='DFTB',
qmcharge=0,
dftb_disper=1,
maxcyc=0,
qmmm_int=1,
/
1 H1 8.67362881 13.27917004 23.81789780
6 CH3 9.10045052 13.75533867 22.93517876
1 H2 8.48295784 14.52715492 22.47572708
... (QM coordinates)
#EXCHARGES
8 O 1.53231990 10.79592514 15.66447353 -0.834000
1 H1 1.96565151 10.58137131 14.83838463 0.417000
1 H2 1.09105611 11.62814236 15.49438477 0.417000
... (MM coordinates and charges)
#END
The result from sander is: DFTBESCF= -2335.9716
The result from sqm is: Heat of formation = -2301.18474934 kcal/mol or Total SCF energy = -16443.26125335 kcal/mol
I have also tried to compare the relative energy between two frames, but the relative energy does not match neither... I have tried amber19, amber22, amber24, and they all give the same results.
But in the end, I would like to know if there could be a way to print the mulliken charges for DFTB/MM calculation that match with what have been done in sander?
Best,
Ge Song
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Received on Wed Mar 26 2025 - 08:00:02 PDT
