Hello everyone.
I'd like to create some additional force fields (FF) for nonstandard molecules, and i don't have enough imagination to specify unique name for every new atom in .par file. (There are about 80 of them.)
I've found that FF parameters are listed in .sgm file.
And according to "NWChem User Documentation Release 5.1.1" (i hope it is still actual in part "segment file format") i can use it in a way:
.sgm file
4.600000
5 4 6 0 0 0 1 1
0.000000
1 C 0 0 0 1 1
CT -0.200000 0.000000
21H 0 0 0 1 1
HC 0.050000 0.000000
32H 0 0 0 1 1
HC 0.050000 0.000000
43H 0 0 0 1 1
HC 0.050000 0.000000
54H 0 0 0 1 1
HC 0.050000 0.000000
1 1 2 0 1
# ^ 1 means to use parameters from the card below
0.209000 2.84512E+05
2 1 3 0 1
# ^ 1 means to use parameters from the card below
0.209000 2.84512E+05
3 1 4 0 1
# ^ 1 means to use parameters from the card below
0.209000 2.84512E+05
4 1 5 0 1
# ^ 1 means to use parameters from the card below
0.209000 2.84512E+05
1 2 1 3 0 0
# ^ 0 means to use parameters from database (.par file ???) ignoring the card below
0.000000 0.00000E+00
2 2 1 4 0 0
0.000000 0.00000E+00
3 2 1 5 0 0
0.000000 0.00000E+00
4 3 1 4 0 0
0.000000 0.00000E+00
5 3 1 5 0 0
0.000000 0.00000E+00
6 4 1 5 0 0
0.000000 0.00000E+00
In this example i changed equilibrium C-H bond length (in par file it is equal to 0.109) in CH4.
However, geometry optimization calculation uses parameters from .par file.
I didn't find any other ways to force NWChem to use FF from .sgm file.
So, the questions are:
Am i missing something? Are there any additional keys i am to use? And is it even possible to specify FF parameters in .sgm file in actual version of NWChem?
BTW: i use NWChem-6.3