Some questions on the QEq charge model



Hi there,
 I wonder if there is anyone in this list familar with the QEq charge
 model.
 Recently I am reading the original QEq paper, and like to post some
 questions about on the CCL. Hope I can get some help from you.
 The attached paper: "Charge Equilibration for Molecular Dynamics
 Simulations", by A. K. Rappe & W. A. Goddard III, J. Phys. Chem. 1991,
 95, 3358-63.
 Q1: There seems to be some typo on the equations in the above JPC
 paper: equation (10) should be CQ=-D, instead of CD=-D(like a
 eigenequation?); and C1j=1, instead of C1j=Qj. One may claim that the
 original equations may still hold with more sophisticated derivations,
 similar to some QM equations, but it will be nice to see how to get to
 those equations. BTW, some references on the paper marked as "to be
 published" seem to be not ever published. Are there any good reasons?
 Q2. If you have implemented it, or ever applied it from commericial
 package(UFF or Cerius2 ?), is there any good sense of its performance?
 In principle, this model should be more accurate than a similar but
 simpler Gasteiger model. The relative speed may be one issue since there
 can be heavy computations needed to get the inverse of a big matrix. Are
 still any benchmark study on the comparison. Not to I know with some
 search over the literature. Maybe there is no good creteria on charge
 models since they are not experimentally measurable, and simulation
 results may be coupled with other issues. Even it's not quite clear from a
 recent paper, PNAS(2002,99,12622) on GPCR and docking, where the charge
 for protein was generated either from CHARMM22 or from the QEq method. It
 is likely the only information on QEq one can find from that paper.
 Q3. I did a little search over google with "CCL, QEq" as keywords.
 Some hits came out. There seem to be lots of questions, but few good
 answers. Just list a few:
   http://www.ccl.net/cgi-bin/ccl/message.cgi?2002+09+23+009
 (even in
 Gaussian)
   http://www.ccl.net/cgi-bin/ccl/message.cgi?1998+01+23+002
   http://ftp.ccl.net/cgi-bin/ccl/message.cgi?1996+01+10+008
   http://www.ccl.net/cgi-bin/ccl/message.cgi?1995+12+17+001
 Anyway, I look forward to your comments on these questions. Any kind
 of information will be highly appreciated.
 Best regards,
 Guosheng Wu
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