Dr. Roitberg,
I'm sorry, I meant to say it converged to the wrong value, i.e. it is off by a few percent (varies depending on the solvent) from the experimental value.
Dr. Chaban,
What I am wondering is, is this acceptable to use differing methods for the different parameters? Is there a paper that describes how to change vdw?
*******************************
Mohd Farid Ismail
Graduate Assistant
Dept. of Chemistry/Biochemistry
University of Oklahoma
Norman 73019
________________________________________
From: Adrian Roitberg [roitberg.ufl.edu]
Sent: Sunday, November 13, 2011 2:55 PM
To: vvchaban.gmail.com; AMBER Mailing List
Subject: Re: [AMBER] Calculate charges using better method/basis set?
What do you mean by "For charges, if I use bcc at first, but the density
would not converge."
It does not converge or it does to the wrong value?
Also, it is not only about charges, the vdw parameters also metter for
the density.
On 11/13/11 3:52 PM, Dr. Vitaly V. Chaban wrote:
> On Sat, Nov 12, 2011 at 1:22 PM, Ismail, Mohd F.<farid.ou.edu> wrote:
>> I am trying to simulate ions in bulk organic solvent. I use gaff for internal parameters. For charges, if I use bcc at first, but the density would not converge. When I use RED, the density is still about 3% higher.
>>
>> Will it be alright if I use higher method or basis set to calculate the charges? I saw some documentation that gaff and amber use HF with 6-31g* for the parameters and charges.
>>
>> I also check the trajectory, but there seems to be no 'stupid' conformation.
>
> The charges are always very sensitive to the ab initio method applied.
> Try MP2 instead, for example. BTW, 3% higher density is not so much
> terrible for most tasks.
>
>
> Dr. Vitaly V. Chaban, 430 Hutchison Hall, Chem. Dept.
> Univ. Rochester, Rochester, New York 14627-0216
> THE UNITED STATES OF AMERICA
>
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> AMBER.ambermd.org
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--
Dr. Adrian E. Roitberg
Professor
Quantum Theory Project, Department of Chemistry
University of Florida
roitberg.ufl.edu
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Received on Mon Nov 14 2011 - 09:00:02 PST
