Re: [ESPResSo-users] OPLS Parameters in ESPResSo

[Axel Arnold]

On 07.08.13 01:12, Jezreel Castillo wrote:
> I would like to ask how to convert OPLS parameters to a form usable in 
> ESPResSo. For example, in dihedral angle interactions, OPLS has a four 
> phase equation, tied to a group of four particles, however in 
> ESPResSo, the equation is tied to a single particle within the 
> dihedral angle. Thank you.

Dear Jezreel,

in ESPResSo, any bond is tied to one particle, but can define an 
interaction of several particles. For a dihedral, that are four 
particles in total, just as in OPLS, which you specify when adding the 
bond. For the order of the particles, please refer to the User's guide, 
there is a picture explaining the order when calculating the angle from 
these for particles.

Espresso's dihedral bond type corresponds to one of the OPLS Fourier 
frequencies, so that you need in total four different dihedrals to model 
a OPLS dihedral. Note that also the phases are alternating in the OPLS 
definition, so that you need to change the phase. By comparing the OPLS 
dihedral force with the Espresso expression, that is straight forward to 
figure our.

Since Espresso is usually not used for atomistic modeling, I am not 
aware of any ready OPLS setup.

Cheers,
Axel

--
JP Dr. Axel Arnold
ICP, Universität Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609