[gmx-users] a question about dihedraltype

[Anton Feenstra]

Lanyuan Lu wrote:

> Hello All,
> I have a question about the directive [dihedraltype] in *.top file. What can I do if I want to define a dihedraltype as a function of all 4 atoms in the dihedral?  In the manual it says that only two atom names was needed (X-A-B-X). What if I want to define a dihedral type (C-A-B-D)? Here the dihedral type depends on all four atoms instead of only inner two.

IIRC, that option was added relatively recently, because the OPLS forcefield
uses it. You can look in the ffOPLS*bon.itp files to see how it's done.

Alternatively, you can skip the definition of [dihedraltype], and add the
parameters directly to the [dihedral] definitions themselfves. For this, you
could also use the #define constructions used in the Gromos forcefields
(ffG43a*bon.itp), like:

#define my_dihedral_type_1 3 90 1.34e3

and, later on,

[dihedrals]
;  i  j  k  l type
    3  5  7  8  1   my_dihedral_type_1
   14 18 21 22  1   my_dihedral_type_1


-- 
Groetjes,

Anton
  _____________ _______________________________________________________
|             |                                                       |
|  _   _  ___,| K. Anton Feenstra                                     |
| / \ / \'| | | Dept. of Pharmacochem. - Vrije Universiteit Amsterdam |
|(   |   )| | | De Boelelaan 1083 - 1081 HV Amsterdam - Netherlands   |
| \_/ \_/ | | | Tel: +31 20 44 47608 - Fax: +31 20 44 47610           |
|             | Feenstra at few.vu.nl - www.few.vu.nl/~feenstra/         |
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