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Re: [ESPResSo-users] OPLS Parameters in ESPResSo

From: Axel Arnold
Subject: Re: [ESPResSo-users] OPLS Parameters in ESPResSo
Date: Wed, 07 Aug 2013 22:50:37 +0200
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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.


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

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