Re: [AMBER-Developers] non-neutral ethane from antechamber

From: David A Case <case.biomaps.rutgers.edu>
Date: Wed, 1 Feb 2012 13:28:37 -0500

On Tue, Jan 31, 2012, Crowley, Michael wrote:

> I wonder if there is something wrong with either my approach or with the
> antechamber process.
> Something as simple as ethane gives charges that do not add to zero
> (+0.00200).

The sqm program only prints Mulliken charges to three decimal places. Then
when atom charges are symmetrized (so the equilvalent atoms have the same
charge), round-off errors can accumulate.

Try changing the qm2_print_charges.F90 file to print an extra digit of
precision for the Mulliken charges. I'm guessing (hoping) that antechamber
will pick that up, and you will get results closer to zero.

....dac


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Received on Wed Feb 01 2012 - 10:30:03 PST
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