CCL: Inquire a cutoff value for degenerate states



 Sent to CCL by: Robert Molt [r.molt.chemical.physics/./gmail.com]
 
It's going to be dependent on the system. We need more information from the original question poser about the context.
 
If I said that two electronic states are separated by 0.1 eV, they are roughly degenerate. If you told me the states were separated by 0.01 eV, I would definitely call those electronic states degenerates. But therein lies the issue: relative to the energy scale of electronic states, 0.01 eV is very tiny. By contrast, like Dr. Abrash noted, 0.01 eV is pathetic for certain spectroscopy studies.
 On 9/18/15 9:27 AM, Abrash, Samuel sabrasha/richmond.edu wrote:
 
 Sent to CCL by: "Abrash, Samuel" [sabrash,+,richmond.edu]
 I don't know the theoretical convention, but from the point of view of a
 spectroscopist (my original training), .01 eV is 81 cm-1, and while states
 separated by 81 cm-1 will begin to exhibit Fermi resonance, they would not be
 considered degenerate.  However, the convention for computational chemistry may
 be based on other arguments.
 Samuel A. Abrash
 Associate Professor, Department of Chemistry
 Coordinator, Environmental Studies Program
 University of Richmond
 sabrash:richmond.edu
 Cell: (804) 363-2597
 www.richmond.edu/~sabrash
 "At the time God created the world and desired to reveal the depth of His
 being from out of the hidden, the light came from darkness and they were joined
 together.  Because of this, out of darkness came the light, and out of the
 hidden came the revealed and out of the good came evil and out of mercy came
 severe judgement, and everything is intertwined with everything else... the good
 inclination and the evil inclination, the right and the left."  The Zohar
 -----Original Message-----
 
 From: owner-chemistry+sabrash==richmond.edu:ccl.net [mailto:owner-chemistry+sabrash==richmond.edu:ccl.net] On Behalf Of Youzhao
 Lan lyzhao a aliyun.com
 
 Sent: Thursday, September 17, 2015 9:01 PM
 To: Abrash, Samuel
 Subject: CCL: Inquire a cutoff value for degenerate states
 Sent to CCL by: "Youzhao  Lan" [lyzhao,+,aliyun.com] Dear all,
    I want to set a small cutoff value for deciding whether two states are
 degenerate.
 Is there a generally acceptted value in a.u. or eV unit for this cutoff?
 e.g., 0.001 a.u. or 0.01 eV?
 Any help will be appreciated.
 Lanhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txt>;
 
 --
 Dr. Robert Molt Jr.
 Visiting Associate Professor of Chemistry
 Department of Chemistry & Chemical Biology
 Indiana University-Purdue University Indianapolis
 LD 326
 402 N. Blackford St.
 Indianapolis, IN 46202