[gmx-users] User-defined potentials.

David van der Spoel spoel at xray.bmc.uu.se
Wed Nov 28 21:26:36 CET 2001

On Wed, 28 Nov 2001, Ram'on Garc'ia Fern'andez wrote:

>On Wed, Nov 28, 2001 at 06:02:45PM +0100, David van der Spoel wrote:
>> On Tue, 27 Nov 2001, Ram'on Garc'ia Fern'andez wrote:
>> >I suppose that the user defined potential is not automatically applied
>> >to all pairs of any type of atoms.
>> Yes it is. Your only variation is the force field parameters.
>I think that I do not understand you. What variation of force field
>parameters is posible? If I am using user-defined potentials, all the
>kinds of atoms will be subject to the same interactions. No parameters
>can change that. What am I overlooking?
The interaction potential is then:

Vij(r) = Aij f(r) + Bij g(r) + (qi qj/4 pi eps0) h(r)

For normal LJ/Coul that would be f(r) = r^-12; g(r) = r^-6; h(r) = 1/r
Your parameters Aij, Bij depend on atomtype, and qi, qj are the charges.

So, same functional form, different forcefield parameters.

Groeten, David.
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel

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