[gmx-users] (no subject)

David spoel at xray.bmc.uu.se
Thu Dec 26 18:12:26 CET 2002

On Thu, 2002-12-26 at 18:14, pqchen at eyou.com wrote:
> Dear gmx-users:
>   In Tinker pakages the improper torsion parameters are different from the
> parameters in gromacs pakages(opls-aa force field)?????
>   For example:
>   In Thinker pakages(opls-aa):
>   improper_Z_CA_X_Y       180.0      2.200(kcal/mol)   2
>   But in gromacs:
>   #define improper_Z_CA_X_Y       180.0      4.60548(KJ/mol)   2
>   which is right?
Apart from the factor 4.184 (x2.2 = 9.2048)
there seems to be a factor of two. This could be due to the different
definitions of the function. I don't know about tinker but in gromacs it
Vimp = 0.5 k_imp(xi - xi0)^2

There is a minute difference left due to the fact that we originally
used a different (wrong) definition of the cal > Joule conversion factor
(yes there are two, the other one is 4.1868!)
This is nothing to worry about, although it will be corrected in future
version of gromacs.

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://xray.bmc.uu.se/~spoel

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