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From: Grzegorz Jezierski <jezierski.theochem.tu-muenchen.de>

Date: Thu, 12 May 2005 18:50:17 +0200

Dear AMBER users,

As a result of a charge fitting procedure using RESP, performed for a

cationic form (1+) of 9N-methylguanine, I could see that calculated

point charges strongly depend on a basis set used and the density of MEP

points specified in Gaussian input, namely:

1) Increasing the 'density of points' parameter "IOp 6/42" from 1 to 6

changed the optimized RESP charges drastically, about 0.1 e on some

atoms. Further increase of the parameter from 6 to 8 gave the changes

0.05 e or lower, and in the same direction (convergence?). Should I go

up with the parameter? What's the precise definition of IOp 6/42? Is it

in 1/(bohr sq.)? The Gaussian manual says "density of points per unit

area in ESP fit" - does this mean the area of one of MEP layers? I kept

all the time the default value for IOp 6/41 (=4). Both geometry

optmization and population analysis was calc. with HF/6-31G*.

2) I then changed the basis set to HF/cc-pVTZ and kept: IOp 6/41=4; IOp

6/42=8. Charges differed (between the two basis sets) by at most 0.05 e,

except for the amino group, where the discrepancy was 0.1 e. Generally,

one see more polarized charge distr. in the case of 6-31G*. Which basis

set is more suitable as regards modeling polarization effects on the

solvent?

Thank you for help.

Grzegorz

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Received on Thu May 12 2005 - 18:53:01 PDT

Date: Thu, 12 May 2005 18:50:17 +0200

Dear AMBER users,

As a result of a charge fitting procedure using RESP, performed for a

cationic form (1+) of 9N-methylguanine, I could see that calculated

point charges strongly depend on a basis set used and the density of MEP

points specified in Gaussian input, namely:

1) Increasing the 'density of points' parameter "IOp 6/42" from 1 to 6

changed the optimized RESP charges drastically, about 0.1 e on some

atoms. Further increase of the parameter from 6 to 8 gave the changes

0.05 e or lower, and in the same direction (convergence?). Should I go

up with the parameter? What's the precise definition of IOp 6/42? Is it

in 1/(bohr sq.)? The Gaussian manual says "density of points per unit

area in ESP fit" - does this mean the area of one of MEP layers? I kept

all the time the default value for IOp 6/41 (=4). Both geometry

optmization and population analysis was calc. with HF/6-31G*.

2) I then changed the basis set to HF/cc-pVTZ and kept: IOp 6/41=4; IOp

6/42=8. Charges differed (between the two basis sets) by at most 0.05 e,

except for the amino group, where the discrepancy was 0.1 e. Generally,

one see more polarized charge distr. in the case of 6-31G*. Which basis

set is more suitable as regards modeling polarization effects on the

solvent?

Thank you for help.

Grzegorz

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Received on Thu May 12 2005 - 18:53:01 PDT

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