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Hi,<br>
<br>
I'm about to simulate a disaccharide in water and have created a
topology/ff-mod based on the 56Acarbo parameters based on gromos
53a6 from<br>
<br>
"A reoptimized GROMOS force field for hexopyranose-based
carbohydrates accounting for the relative free energies of ring
conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic
linkage conformers."<br>
Hansen, H. S.; Hünenberger, P. H. <i>Journal of computational
chemistry</i>. 2010.<br>
doi: 10.1002/jcc.21675<br>
<br>
I'm having troubles understanding how to implement the special 1-5
LJ interactions (N2 and N5, p 1008 in the article) used in that
paper. I tried to use the [ pairs_nb ] section in the molecule
topology since I believe the [ pairs ] section is for 1-4
interactions only, but with that grompp failed with the following
error:<br>
<br>
Fatal error:<br>
Invalid case in switch statement, file topio.c, line 905<br>
For more information and tips for troubleshooting, please check the
GROMACS<br>
website at <a class="moz-txt-link-freetext" href="http://www.gromacs.org/Documentation/Errors">http://www.gromacs.org/Documentation/Errors</a><br>
<br>
This error seems to disappear when the section is commented out.<br>
<br>
Thus I have a couple of questions that someone might be able to
answer:<br>
<br>
Can I use the [ pairs ] section for 1-5 interactions,<br>
or do you have any other suggestions (I'm modifying a copy of
gromos53a6.ff/)? <br>
What is the [ pairs_nb ] used for?<br>
<br>
Below follows a relevant section of my molecule.itp, the charges are
there because that is how pairs_nb looks in the manual. The
variables N1-N5 are defined in the ffbonded.itp file.<br>
<br>
[ pairs ]<br>
; ai aj funct <br>
1 4 1 <br>
1 12 1 <br>
1 14 1 <br>
2 5 1 <br>
2 11 1 <br>
2 13 1 <br>
3 6 1 <br>
3 12 1 <br>
4 13 1 <br>
5 8 1 <br>
6 11 1 <br>
6 15 1 <br>
6 19 1 <br>
7 8 1 <br>
7 10 1 <br>
8 9 1 <br>
10 25 1 <br>
14 17 1 <br>
14 24 1 <br>
14 26 1 <br>
15 18 1 <br>
15 27 1 <br>
16 19 1 <br>
16 26 1 <br>
17 27 1 <br>
18 21 1 <br>
18 24 1 <br>
18 25 1 <br>
20 21 1 <br>
20 25 1 <br>
21 22 1 <br>
23 25 1<br>
9 6 1 N3 ;C6 C1<br>
9 2 1 N3 ;C6 C3<br>
22 15 1 N3 ;C12 C8<br>
22 19 1 N3 ;C12 C11<br>
25 2 1 N4 ;O9 C3<br>
25 4 1 N4 ;O9 C5<br>
10 3 1 N4 ;O2 C4<br>
7 6 1 N4 ;O3 C1<br>
7 4 1 N4 ;O3 C5<br>
8 1 1 N4 ;O4 C2<br>
25 16 1 N4 ;O9 C9<br>
23 15 1 N4 ;O1 C8<br>
23 17 1 N4 ;O1 C10<br>
20 17 1 N4 ;O7 C10<br>
20 19 1 N4 ;O7 C11<br>
21 14 1 N4 ;O8 C7<br>
<br>
[ pairs_nb ]<br>
11 3 1 0.42 0.232 N2 ;HO2 C4<br>
11 5 1 0.42 -0.464 N2 ;HO2 O5<br>
12 6 1 0.42 0.464 N2 ;HO3 C1<br>
12 4 1 0.42 0.232 N2 ;HO3 C5<br>
13 1 1 0.42 0.232 N2 ;HO4 C2<br>
13 5 1 0.42 -0.464 N2 ;HO4 O5<br>
26 19 1 0.42 0.464 N2 ;H11 C11<br>
26 17 1 0.42 0.232 N2 ;H11 C10<br>
27 14 1 0.42 0.232 N2 ;H12 C7<br>
27 18 1 0.42 -0.464 N2 ;H12 O6<br>
25 9 1 -0.464 0 N5 ;O9 C6<br>
7 9 1 -0.642 0 N5 ;O3 C6<br>
23 22 1 -0.464 0 N5 ;O1 C12<br>
20 22 1 -0.642 0 N5 ;O7 C12<br>
<br>
Thanks in advance!<br>
<br>
Regards<br>
Jon<br>
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