G03: LANL2DZ basis set for Se Te...

[Wai-To Chan <chan/at/curl.gkcl.yorku.ca>]

<<<<<<<<<<<
 Hello CCLers
 I get the following warning while using LANL2DZ basis set for Se or
 (Te) atom  in Gaussian 03.
 " Warning!  Se atom    1 may be hypervalent but has no d functions."
 In the Gaussian book (Exploring Chemistry.. Foresman and Frisch) I saw
 something about  adding diffuse functions manually with a file called
 "plus.gbn"
 do I have to add  d functions manually?  or is the LANL2DZ basis set
 good enough. I am mainly interested in the structure of molecules like
 (H2SeO4)
 I saw a thread titled "generating or augmenting basis sets" from last
 year on ccl.net but could not find the answer. Thanks a lot for your
 help
 >>>>>>>>>>>>>
   I've used ECP basis sets like lanl2dz and SDD for transition metal
 and main group elements. I don't recall ever seeing messages
 like this. I guess the warning is caused by the unsually large number
 atoms linked to the Se atom.
   I've read reports of lanl2dz calculations involving augmentation
 of the ECP basis with polararization and diffuse function. But
 I can't think of a source of the additional basis functions to
 use. Gaussian has full-electron basis set like 6-31+G(d,p)
 for Se but I don't know if transferring the d function to
 lanl2dz is a good idea.
 In case that is what you want the way
 to do this is simply using the option "extrabasis" to
 add the extra basis functions to the specified
 atom. The older versions of gaussian come in with
 a basis set library which you can easily look up for the
 exponents of the polarization and diffuse functions.
 With the recent versions you have to extract the basis
 set information manually.
   As an illustraction if I want to augment Se with
 the d function from 6-311G** I will first run a job like
 rhf/6-311G(d,p) gfinput (or gfprint)
 on the above molecule. The gfinput option will
 print out the basis set details in a convenient
 format.  I will then run a job like
 rhf/lanl2dz extrabasis
   This extrabasis option requires you to append the
 basis function details to the end of your input file.
   Without any augmentation lanl2dz and SDD will use the
 D95 basis set for the light atoms. So you may consider
 the use of polarization functions
 > from D95** instead of 6-31+G* or 6-311+G*. My experience
 is that augmentation of the light atoms alone with polarization
 functions from D95** generally results in significant improvement
 of the performance of the ECP basis for geometry optimization
 particularly on the bond distance between the heavy
 atom and the ligand. But I don't know what the appropriate approach
 is for the augmentation of the heavy atom.
 Wai-To Chan