In addition, Chimera does its force-field-based charge assignment by looking up the residue/atom names in a table. The GLYCAM forcefield defines over 1400 residue names, most of which are not PDB standard residue names. For instance, PDB residue VEA is a porphyrin, whereas in GLYCAM it is obviously a polysaccharide. Therefore, the forcefield-based charge assignment mechanism in Chimera would have to be significantly reworked in order to properly support the GLYCAM files while still handling standard PDB residues that have names found in the GLYCAM files. Even if this work was done, you (the user) would have to ensure that your structure used the proper GLYCAM residue and atom names rather than, e.g., GLC (PDB residue name for alpha-D-glucose) which is not found in the GLYCAM files!

Eric Pettersen

UCSF Computer Graphics Lab

http://www.cgl.ucsf.edu

On Dec 28, 2012, at 11:39 AM, Elaine Meng wrote:

Hi John,
Sorry, currently Glycam isn't included in the parameter lookup by Chimera. Here are details on which parameter files are used for each of the force field choices:

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/minimize/minimize.html#limitations>

You can assign charges manually, but it is more labor-intensive:
<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/minimize/minimize.html#user-specified>

Elaine
-----
Elaine C. Meng, Ph.D.
UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
Department of Pharmaceutical Chemistry
University of California, San Francisco

On Dec 26, 2012, at 11:27 PM, john Kerk wrote:

Dear Users
I want to assign the partial charges of a glucose molecule using chimera-1.7 but I can not find this force field in Add charge suite although the GLYCAM force field files are existing under amber12.
can I get help
wishing merry Christmas ,
John

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