On basis sets for calculating thermochemistry properties

From: Wai-To Chan <chan*at*curl.gkcl.yorku.ca>
Subject: On basis sets for calculating thermochemistry properties
Date: Sun, 8 Jun 2003 01:42:18 -0400 (EDT)

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 Dear all,
 I am calculating thermochemistry properties by Gaussian DFT method. Can
 anyone give me some suggestions on basis sets for the calculation?
 Which is the minimum basis set I can use in this calculation is
 reasonable? With small basis sets (sto-3g, 3-21g), which one can get
 better results for thermochemistry properties by Gaussian DFT method?
 Thanks to you all,
 Holly
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 I used the xalpha/3-21g method for geometry optimization
 of LARGE molecules in the past and got some decent results. But
 sto-3g and 3-21g won't be a good choice for reliable thermochemistry
 calculation with Hybrid DFT method like B3LYP. Use a basis set at least
 as large as 6-31+G(d)/6-31+G(d,p). The inclusion of '+' can make a difference.
 You may refer to
    J. Phys. Chem. A, (2003) vol 107 pg 1384-1388 by Lynch, Zhao and Truhlar
 for an assessment of the accuracy of the MPW1PW91/6-31+G(d,p) method.
 Wai-To Chan