CCL:G: how to choose basis set for optimization of organic molecular
- From: Herbert Fruchtl
- Subject: CCL:G: how to choose basis set for optimization of organic
- Date: Fri, 30 Jul 2010 10:14:20 +0100
Sent to CCL by: Herbert Fruchtl [herbert.fruchtl ~~ st-andrews.ac.uk]
If you want a series of basis sets with systematic convergence to the
(complete basis set) limit, look at the Dunning basis sets (cc-pvdz,
etc.). For a single small molecule you probably don't need extra
sets (aug-cc-pvNz, or "+" with Pople basis sets).
What is probabbly even more important is the method. If you use DFT,
go for one
of the more modern meta-hybrid functionals (e.g. M06-2X). The best
ab initio method for molecules of this size would be CCSD(T), but a
optimization with that can get expensive. Gaussian might not be the
appropriate program in that case.
Heng Zhang chemzhh..163.com wrote:
Sent to CCL by: "Heng Zhang" [chemzhh,,163.com]
I am optimizing a molecular C8H8ClNO. There may be two isomers whose energy is
very close (less than 0.45 kcal/mol by using 6-31+g*). I want to compute the
accurate structure and energy of this molecular by using high precision basis
set. Can any one give some suggestions? Thanks.
By the way, in that kind of calculation using Gaussian, is there some other
things that should be paied attention to.
Senior Scientific Computing Officer
School of Chemistry, School of Mathematics and Statistics
University of St Andrews
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