CCL: Clarification for restricted/unrestricted spin in TDDFT

From: "jacqueline cawthray" <jcawth01()gmail.com>
Subject: CCL: Clarification for restricted/unrestricted spin in TDDFT
Date: Mon, 9 Jan 2012 12:46:04 -0500

 Sent to CCL by: "jacqueline  cawthray" [jcawth01_+_gmail.com]
 Hi
 I'm trying to calculate the UV spectra of some transition metal complexes
 involving Cu2+, Fe3+ and Zn2+. I have successfully been able to calculate Zn2+
 complexes which show good agreement with experimental results. However I am
 not having much luck with Cu2+ or Fe3+. I understand I may need to change
 basis sets (I have been using B3LYP/6-31+g(d,p) and am currently trying with
 LanL2Dz on the metal) but have read about using unrestricted B3LYP. Can
 someone possibly explain (in laymans terms) what the difference between
 restricted and unrestricted is so I can decide which to use?
 Thanks
 Jacquie