Definition impropers x-plor vs charmm

Willem Paul van Hoorn W.P.vanHoorn at
Fri Jan 19 09:57:21 EST 1996

I try to transfer some quanta/charmm parameters into X-plor. When I
asked the energy of a conformation in Quanta/CHARMm and X-plor all
energy components are the same, except for the improper angle energy.
When looking into the CHARMM/X-plor manuals I found out the the definition
of dihedral angles is slightly different:
CHARMM: kijl angle between kij and kjl planes
Xplor : ijkl angle between ijk and jkl planes
Together with Xplor some CHARMM parameter/topology files are shipped.
When I compare the Xplor version with the original CHARMM version,
the improper parameters in the parameterfile are exactly the same, and
the residue definitions in the topology file too (Some impropers which 
are present in the CHARMM file are missing in the Xplor file). 
Who knows how impropers are defined in Xplor (and CHARMM)?

thanks in advance,

Willem Paul.

 (ir) Willem Paul van Hoorn      
 University of Twente                   e-mail: wphoorn at 
 Laboratory of Organic Chemistry        phone : (+31)53-4892955
 P.O. Box 217                                   (+31)53-4892980
 7500 AE  Enschede, The Netherlands     fax   : (+31)53-4894645

More information about the X-plor mailing list