[gmx-users] Selecting force field for simulation in vacuum

David van der Spoel spoel at xray.bmc.uu.se
Thu Dec 4 14:23:49 CET 2008

Justin A. Lemkul wrote:
> GROMOS and OPLS were derived for condensed-phase properties, so none of 
> those will be useful.  I know nothing about ENCAD, however, but I do not 
> often see it in the literature.

This depends on the kind of substance you are simulating. If 
polarization is relatively unimportant (e.g. in alkanes) you can use the 
same parameters without problems. The Trappe (united atom, 
non-polarizable) force field is extensively used in liquid/vapor 
equilibrium with good success, so one should not be to categorical about 
these things. One can test e.g. the heat of vaporization and the second 
virial coefficient to test vacuum properties.

For proteins we have used both OPLS andn GROMOS96, but the problem there 
is that it is hard to verify the results.

> -Justin
> Nuno Azoia wrote:
>> Hello everyone!
>> I'm having some problems for selecting force field for a simulation in
>> vacuum. I'm using version 4.0.2.
>> According to pdb2gmx man page (pdb2gmx -h)
>>         DESCRIPTION
>>         -----------
>>         This program reads a pdb file, reads some database files, adds
>>         hydrogens to
>>         the molecules and generates coordinates in Gromacs (Gromos)
>>         format and a
>>         topology in Gromacs format. These files can subsequently be
>>         processed to
>>         generate a run input file.                 The force fields in 
>> the distribution are currently:
>>                 oplsaa OPLS-AA/L all-atom force field (2001 aminoacid 
>> dihedrals)
>>         G43b1  GROMOS96 43b1 Vacuum Forcefield         G43a1  GROMOS96 
>> 43a1 Forcefield         G43a2  GROMOS96 43a2 Forcefield (improved 
>> alkane dihedrals)
>>         G45a3  GROMOS96 45a3 Forcefield         G53a5  GROMOS96 53a5 
>> Forcefield         G53a6  GROMOS96 53a6 Forcefield         gmx    
>> Gromacs Forcefield (a modified GROMOS87, see manual)
>>         encads Encad all-atom force field, using scaled-down vacuum
>>         charges
>>         encadv Encad all-atom force field, using full solvent charges
>> Ok. I would like to use G43b1, but when I run
>> pdb2gmx -f protein.pdb -o protein.gro -p protein.top -n system.ndx -i
>> posre.itp  -inter -ignh
>> I just get this options, with no possibility for choosing G43b1:
>>         Select the Force Field:
>>          0: GROMOS96 43a1 force field          1: GROMOS96 43a2 force 
>> field (improved alkane dihedrals)
>>          2: GROMOS96 45a3 force field (Schuler JCC 2001 22 1205)
>>          3: GROMOS96 53a5 force field (JCC 2004 vol 25 pag 1656) 
>>          4: GROMOS96 53a6 force field (JCC 2004 vol 25 pag 1656) 
>>          5: OPLS-AA/L all-atom force field (2001 aminoacid dihedrals)
>>          6: [DEPRECATED] Gromacs force field (see manual)
>>          7: [DEPRECATED] Gromacs force field with hydrogens for NMR
>>          8: Encad all-atom force field, using scaled-down vacuum charges
>>          9: Encad all-atom force field, using full solvent charges   
>> I search on the mailing list for some solution and I get this message
>> from Berk Hess
>> (http://www.gromacs.org/component/option,com_wrapper/Itemid,165/)
>>         The GROMOS96 G43b1 "vacuum" force field has been removed.
>>         This confusing "vacuum" naming of this force field could make 
>> people
>>         think that this force field was optimized for real vacuum 
>> simulations,
>>         whereas it is actually G43a1 with neutralized charged residues.
>>         This force field has never been used seriously.
>> Now I'm confused! Ok, there is no more G43b1.
>> So I would like to ask witch force field I can use for simulations in 
>> vaccum? If I search on the mailing list I get the advice of using G43b1.
>> Can anyone help me on this.
>> And just another small thing. Maybe it would be good to remove the 
>> reference to G43b1 on the pdb2gmx man page.
>> Thank you in advance.
>> Nuno Azoia
>> --
>> Nuno Gonçalo Azoia Lopes
>> Laboratório de Investigação em Acabamento
>> Departamento de Engenharia Textil
>> Universidade do Minho
>> Campus de Azurém
>> 4800-058 Guimarães
>> Portugal
>> Tel: +351 253 510 280 - Ext: 517 289
>> Fax: +351 253 510 293
>> Mobile: +351 965 382 487
>> E-mail: nazoia at det.uminho.pt
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David van der Spoel, Ph.D., Professor of Biology
Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205. Fax: +4618511755.
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se

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