[gmx-users] Re:gromos torsion param

[rob yang]

Thank you David.
Does anybody have any experiences adding more torsion terms in gromos? What 
would be the format in the .top files? Thank you in advance.

Rob


>From: David van der Spoel <spoel at xray.bmc.uu.se>
>rob yang wrote:
>>Hello,
>>I've got a rudimentary question about gromos torsion parameters.
>>
>>the gromos parameter is of the following format:
>>gd_1           2.67             -1.0            1
>>name      force constant  phase shift    multiplicity
>>
>>>From the gromos paper, they've listed the torsion terms as
>>K*[1+cos(phaseshift)cos(multiplicity*dihedral)
>>
>>In a given .top file, one would parameterize the torsion of i, j, k, l by:
>>i j k l gd_1
>>
>>so my question is that: does that mean for any torsion, there's only *one* 
>>term associated with it in the gromos forcefield? In contrast,  oplsa 
>>allows up to 6 terms in the following form:
>>V1/2(1+cos(x))+V2/2(1-cos(2x)) + V3/2(1+cos(3x))...
>>
>Yes that's correct, although you could in principle add multiple torsions I 
>think.
>