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differences in charmm and QM interaction energies
#1265 04/16/04 12:39 PM
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Which range is acceptable between ab initio and empirical interaction energies of model compound and water? Based on the parameter sets of“alpha-D-glucopyranose”, I built the parameter sets of “beta-D-galactose” with the only change of IC, and got the interaction energies between galactose and water, the largest difference between ab initio and empirical interaction energies is up to about 1.5kcal/mol, are they OK? in my opinion, the atomic partial charges and parameters of glucopyranose should be suitable for galactose, but this big difference let me worried, should I optimized them? Thanks a lot!

Last edited by alex; 04/22/04 05:25 PM.
Re: difference range of interaction energies?
shouqinlv #1266 04/22/04 05:24 PM
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Ideally, the difference between the empirical interaction energies and the target
QM values should be in the range of tenths of kcal/mol. However, it is often
necessary to balance between different interaction orientations such that one
orientation may be to favorable while another is not favorable enough. In such
situations, I try to adjust the charges such that the average difference of all the
interaction energies is close to zero.

Note that the sugar hydroxyl charges are based on methanol and ethanol; they
have never been rigorously tested in the context of the sugars. Thus, you may
find some large differences. We hope to produce some better sugar parameters
in the not to distant future.


School of Pharmacy
University of Maryland
20 Penn Street
Baltimore, MD, 21201

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