CCL:G: sulfur with 6-31G** and lanl2dz

[Jamin Krinsky <jamink^^^berkeley.edu>]

 Sent to CCL by: Jamin Krinsky [jamink]^[berkeley.edu]
 Zineb,
 For clarification, LANL2DZ uses D95V for Z<11, which is ALMOST
 comparable to 6-31G(d,p), so it does have polarization. That being
 said (and I don't think you were suggesting this but just in case),
 you don't want to compare the energies using the two basis sets
 anyway. Using an ECP basis for S is not generally ideal (partially
 because LANL2DZ does NOT put polarization on P, S, etc.), you may want
 to use 6-31G(d,p) for everything up to Ar and LANL2DZ for the
 remainder. I assume you're using Gaussian, so you might want to check
 out a tutorial for setting up custom basis sets here:
 http://glab.cchem.berkeley.edu/glab/faqs/gauss_custombasis.html
 Jamin
 On Wed, Sep 15, 2010 at 9:51 PM, Eric B. Isaacs ebisaacs-.-gmail.com
 <owner-chemistry|-|ccl.net> wrote:
 >
 > Sent to CCL by: "Eric B. Isaacs" [ebisaacs.|-|.gmail.com]
 > Hi Zineb,
 >
 > As far as I know the LANL2DZ basis set is actually 6-31G for atoms with
 > Z<11, so if all the atoms i quinoxaline n your other derivatives meet
 this
 > criterion then you should expect the total energies to be pretty close to
 > 6-31G(d,p) -- there should just be some small change
 >>
 >> from the addition of polarization functions. In contrast, when you're
 >
 > using the pseudopotential/effective core potential with the
 > sulfur-containing molecule some of the sulfur electrons are not being
 > treated explicitly, so the total energy should change significantly.
 >
 > Eric
 >
 > On Sep 15, 2010, at 7:15 PM, zouzou adnani zinebeladnani-*-hotmail.com
 > wrote:
 >
 >>
 >> Sent to CCL by: "zouzou  adnani"
 [zinebeladnani#,#hotmail.com]
 >> hi
 >> I'm working on the geometry optimisation of the some quinoxaline
 >> derivatives using different basis set , in most of my systems I have
 almost
 >> the same energies with both 6-31G(d,p) and lanl2dz basis sets, except
 in
 >> those containing sulfur atoms, can anyone tell me why?
 >> Thanks for taking the time to read this!
 >> Regards,
 >> Zineb el adnani>    >       >
 > Job: http://www.ccl.net/jobsConferences:
 > http://server.ccl.net/chemistry/announcements/conferences/>;
    >
 >
 >
 --
 Jamin L Krinsky, Ph.D.
 Molecular Graphics and Computation Facility
 175 Tan Hall, University of California, Berkeley, CA 94720
 jamink|-|berkeley.edu, 510-643-0616
 http://glab.cchem.berkeley.edu