CCL:G: Re: Diffuse function as a necessay evil

["mi yang" <agri_chemist^_^yahoo.com>]

 Sent to CCL by: "mi  yang" [agri_chemist*|*yahoo.com]
 > Sent to CCL by: "mi  yang" [agri_chemist^yahoo.com]
  Hello CCL colleagues,
  I want to discuss about basis set with diffuse function. Normally, with anionic
 or excess electron species during the calculation of CIS (Opt) or TD-DFT the
 diffuse function is consider essential but often it very difficultly converge
 the SCF (sometimes not at all) even with systems less than three benzene rings.
 Now My questions are:
  1- I am dealing with optical properties of halogen ions (medium size systems)
  and often use 6-31+G* basis set in which diffuse function is often proves for
 me a necessary evil. Is there other equivalent basis set having diffuse function
 and also easy to converge in CIS or TD-DFT calculations?
  2- Now my idea is How it would be If I will use the split basis set (Gen) I
 mean diffuse function for halogen ions only and without diffuse for other atoms
 in a system?
  Any related material or comment would be highly apriciated.
 Mi
  agri_chemist[#]yahoo.com
 ****************************************************************
 "Dipankar Roy dipankarroy%a%iitb.ac.in"  wrote:
 >
 > Sent to CCL by: "Dipankar Roy" [dipankarroy{=}iitb.ac.in]
 > Hi,
 > You can use Duuning's augmented basis sets.
 > For Gaussian program, you can use Gen keyword for defining different basis
 > set for different atoms. Gaussian web sites and manual contains detailed
 > explanation for the same.
 >
 > Hope this may help,
 > Dipankar Roy
 >
 >
 > ***********************************************
 >    Dipankar Roy
 >    Graduate Student of Prof. R. B. Sunoj
 >    Computational Chemistry Laboratory
 >    Dept. of Chemistry
 >    Indian Institute of Technology, Bombay
 >    India - 400076
 >    Phone: +91-22-2576-4130(lab)
 ********************************************************
 Dear Colleague! Thank you for reply
 You mean to say that Dunning is more efficient and economical from computational
 cost but there are different types of Dunnig basis sets on EMSL e.g. Dunning-Hay
 Diffuse, "DZ (Dunning)" or "DZP + Diffuse (Dunning)" which
 can be equivalet (round about) to 6-31+G*.
 Secondly, I knew the use of Gen basis set but my question was How it would be If
 I will use the split basis set (Gen) I mean diffuse function for halogen ions
 only and without diffuse for other atoms in a system? Because I didnt find any
 work in which Gen is used for separation of diffuse function?
 agri_chemist###yahoo.com