AMBER Archive (2009)

Subject: [AMBER] Different optimized structures with HF and B3LYP

From: Sanghwa Han (
Date: Fri Oct 02 2009 - 02:50:10 CDT

Dear Colleagues,

I am trying to obtain a geometry optimized structure of C6H5-O-SO3- (singly
deprotonated form of phenyl hydrogen sulfate).

When optimized with HF/6-31G*, the dihedral angle of C-C-O-S was close to 90
degrees but with B3LYP/6-31G* or MP2/6-31G* it was close to 0 degrees.

In addition, the C-C-O-S torsional profile had a minimum at 90 degrees with
HF/6-31G* but at 0 degrees with B3LYP/6-31G* or MP2/6-31G*.

Molecular mechanics minimization (for example, that in PRODRG site) yielded
a structure with 0 degrees.

Is it possible to obtain completely different optimized structures with
different QM methods?

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