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Selenium basis set Date: 2007/02/16 10:59 Name: shyam   <shyamuh@gmail.com> Dear all, Iam having trouble with giving a basis set to selenium atom. I know it has 6 valence electrons...but do i use a s2p2d2 or what? kindly help. thanks shyam

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Re: Selenium basis set ( No.1 ) Date: 2007/02/20 19:48 Name: Vasilii.Artyukhov You can use any basis set starting from s1p1. This one will have one s function and three p functions ('px', 'py', and 'pz', although this designation has not much of a meaning for a free atom). Then, in a free atom, the wavefunctions of two electrons would be described by the s-like function, and the other four would be described by three p-likes. Adding more basis functions is needed to allow some radial flexibility (and angular, if you add d-functions), similarly to the multiple-zeta concept of Gaussian basis sets. So, the answer to your question is, your basis must contain at least one s and one p function, but you would perhaps want to add more of them and even some d functions to improve your results. The idea is to check whether an additional d function gives you more benefit than an additional sp function pair. For instance, s1p1d1 seems to be better than s2p2. An remember that there's a very nice orbital optimization feature, so you can optimize an s5p5d5 basis to something like s2p2d1 and have very nice results at a moderate price.

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