Re: CCL:Dipole Moment



Antonio,
 	I do not know if this is the BEST methodology (other responses
 will give you some idea about that) but a good way to do this is to
 optimize your molecules with correlated methods to give you a very high
 quality geometry and then perform a single-point calculation with Sadlej's
 basis set:
 	Sadlej, A. J. Collect. Czech. Chem. Commun. 1988, 53, 1995.
 			(where 1988 is the publication year)
 whereby you obtain the dipole moments (also quadrupole moments) very
 accurately when compared to experiment.  Some work I was involved in a few
 years ago, we calculated these types of things for nucleic acid bases:
 	J. Phys. Chem. 1996, 100, 18875.
 and could only afford MP2 geometry optimizations with 6-31G(d,p) and that
 actually gave nice results when compared to geometrical details from
 experiment.  You will note that the Pople series of basis sets, whilst
 good for geometry optimizations, give miserable results for electric
 properties of molecules.  You will, however, find quite a lot of people
 who seem to "sneek through the cracks" and publish junk results for
 these
 types of things.  You would be well advised to stick close to Physical
 Chemistry/Theory type articles.
 	There are a few people who choose to perturb 6-31G (or some
 variation of this) and they have improved the accuracy of the dipole
 moment but nowhere near as well as Sadlej's will. I would not personally
 recommend you do this, but if you are interested in seeing an example of
 this then I refer you to:
 	Sponer, J.; Hobza, P. J. Phys. Chem. 1994, 98, 3161.
 Regards,
 Trevor D. Power
 Department of Chemistry
 University of North Texas
 NT Station, Box 305070
 Denton, Texas 76203-5070
 tdp0006 : at : unt.edu
 On Fri, 3 Nov 2000, Dr. Antonio Buljan wrote:
 > Dear CCLers,
 >
 > What is the best methodology to calculate
 > dipole moments in diatomic molecules?
 > (for example: CO, LiH, etc.)
 >
 > Dr. Antonio Buljan
 > Departamento de Fisico Quimica
 > Universidad de Concepcion
 > Casilla 160-C
 > CHILE
 >
 >
 >
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