From owner-chemistry@ccl.net Sat Sep  1 15:26:00 2007
From: "Chang Ge JI cgji(0)itcc.nju.edu.cn" <owner-chemistry-$-server.ccl.net>
To: CCL
Subject: CCL:G: Cutoff used in MP2 correction to the CASSCF calculation in Gaussian03
Message-Id: <-35067-070901040811-26614-f7WBaqZVmoUfBgrx3V2Zkw-$-server.ccl.net>
X-Original-From: "Chang Ge JI" <cgji++itcc.nju.edu.cn>
Date: Sat, 1 Sep 2007 04:08:08 -0400


Sent to CCL by: "Chang Ge JI" [cgji%x%itcc.nju.edu.cn]
HI,folks.,

I tryed to study vertical excitation energy of small organic molecule using 
 
CASSCF+MP2 method ( GAUSSIAN03 package)

During the  MP2 correction calculation to the MCSCF energy , there exist one parameter for configuration cutoff for mp2 
IOp(5/52).

The default cutoff is 0.1 . If i use the default cutoff in Gaussian03, some times i got a zero correction energy for none of the configurations was selected for mp2 correction.

If i choose different cutoff , the calculated vertical excitation energy differ a lot .

Can you please share me some experience on choosing of this parameter ...


 Thank you in advance.......