In addition to finding a basis set for Xe, it’s important = to understand why 6-31G is not extended as far as Xe. For very heavy = atoms such as Xe, the very large nuclear charge means that core electrons a= re moving at speeds at which special relativity has an important effect on = the results. One such results is that the bond lengths calculated for= very heavy atoms using the Dirac equation, which includes the effect of sp= ecial relativity are shorter than those from the Schrodinger equation, whic= h ignores relativistic effects. This shortening of bond lengths is ca= lled relativistic contraction.

<= span style=3D'color:blue'>The way that this is handled for most of us is to= use basis sets in which the functions for the core electrons are replaced = by potential energy functions which have been calculated using the dirac eq= uation. These are called relativistic effective core potentials, alth= ough they are usually simply referred to as ECPs. The valence electro= ns are treated with normal basis functions since electron shielding means t= hat their average velocities are far from the relativistic limit. Usi= ng these ECP basis sets has two attractive outcomes. First, it means = that the relativistic effects are accounted for. Second, since the la= rge number of core electrons is replaced by a relatively small number of po= tential functions, the computational expense is substantially reduced compa= red to all electron bases.

I hope this is helpful.

Best regards,

Sam

<= p class=3DMsoNormal>

Samuel A. Abrash
Departm= ent of Chemistry
University of Richmond
Richmond, VA 23173
Phone:&= nbsp; 804-289-8248
Fax: 804-287-1897
E-mail: sabrash : richmond.edu
Web-page: http://www.richmond.edu/~sab= rash

"In 1893 C= harles Hinton left Japan to become a mathematics instructor at Princet= on University, where he invented a baseball-pitching machine that used= gunpowder to propel the balls, like a cannon. After several accident= s, the device was abandoned and Hinton lost his job ..." Terry Pratche= tt, Ian Steward and Jack Cohen, The Science of Diskworld III

From: owner-chemistry+sabrash=3D=3Drichmond= .edu : ccl.net [mailto:owner-chemistry+sabrash=3D=3Drichmond.edu : ccl.net] = On Behalf Of dipankar roy theodip(a)gmail.com
Sent: Thursday,= December 01, 2011 7:35 PM
To: Abrash, Sam
Subject: CCL= :G: Basis sets for Xe

Hi,

= You can try basis sets like def2-TZVP or modified correlation consistent basis sets of Dunning with= ECPs. You can get them from EMSL basis set exchange.

best,

= Dipankar Roy

-----------------------------------

Dr. Dipankar Roy

Research Associate

H= unter College (CUNY)

695 Park= Avenue

New York, USA

NY-10065

-----------------------------------

<= o:p>

On Thu, Dec 1, 2011 at 4:55 P= M, Alec Young alecyoung76(0)yahoo.com <= owner-chemistry*_*ccl.net&= gt; wrote:

Sent to CCL by: "Alec Young" [alecyoung76[#]yahoo.com]
Deal All,

= I used M052X/6-31+G* in gaussian trying to optimize the distance between Xe= and a ethylene. And I got this error:

"Atomic number out of ra= nge for 6-31G basis set."

What basis set can I use?

Than= ks,

-Alec

-=3D This is automatically added to each me= ssage by the mailing script =3D-<br

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