CCL:G: SCF converge problem for ROHF calculation in G03 /09

 Sent to CCL by: Mariusz Radon [mariusz.radon::gmail.com]
 Hello,
 Indeed, (lack of) convergence in ROHF is a problem. I would advice you to try:
  - different (smaller) basis set - than use converged solution as
 guess for the larger basis - as was already suggested;
  - play a little bit with level shift (vshift);
  - if possible, try also a different software, in particular
 Schrodinger's Jaguar, esp. if your system is a transition metal
 complex.
 Are your calculations true ROHF or rather RO-DFT? If DFT, you may try
 with a different functional. I have heard that it might be easier to
 converge RO-DFT with hybrid than with non-hybrid functional (but I
 don't know how much it can be helpful in practice). You may also try
 the 100% of the exact exchange i.e. true ROHF calculations. If these
 calculations converge, you will be able to provide a better guess to
 your favorite functional.
 With best regards,
 Mariusz Radon
 2010/1/6 John McKelvey jmmckel%x%gmail.com <owner-chemistry|,|ccl.net>:
 >
 > Sent to CCL by: John McKelvey [jmmckel**gmail.com]
 > It is not stated what basis was used.  On the assumption that as basis
 > sets get larger convergence difficulties may increase, there is always
 > the possibility that starting with smaller basis sets where
 > convergence occurs and then slowly increase the size of the basis set
 > while using the "guess=read" option, which will pick up the
 previous
 > SCF vectors as a starting guess.
 >
 >
 > John McKelvey
 >
 > 2010/1/5 xunlei ding dingxunlei###gmail.com
 <owner-chemistry.:.ccl.net>:
 >>
 >> Sent to CCL by: xunlei ding [dingxunlei|a|gmail.com]
 >> Dear All,
 >>
 >> We know that the SCF converge problem for RHF or UHF calculations can
 >> be solved by "qc" and many other ways.
 >>
 >> But the keywords "qc" and "fermi" can not be used
 in G03/09 for
 >> restrict open shell calculations (such as ROHF).
 >>
 >> In G09, it is said in the manual that "For difficult-to-converge
 ROHF
 >> wavefunctions, where QC cannot be used, add Use=L506 to the route
 >> section." But it seems not work in my test.
 >>
 >> Then, how to solve the SCF converge problem for ROHF calculation?
 >>
 >> Thanks you for your consideration!
 >>
 >> --
 >> ------------------------------------------------------
 >> Xun-Lei Ding (丁迅雷)
 >> Associate Research Professor of Physical Chemistry, Ph.D
 >> State Key Lab for Struct. Chem. of Unstable and Stable Species
 >> Institute of Chemistry, Chinese Academy of Sciences
 >> Zhongguancun North First Street 2，
 >> Beijing 100190, P. R. China
 >> Phone 86-10-62568330
 >> Fax   86-10-62559373
 >>
 >>
 >>
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 >>
 >
 >
 >
 > --
 > John McKelvey
 > 10819 Middleford Pl
 > Ft Wayne, IN 46818
 > 260-489-2160
 > jmmckel.:.gmail.com
 >
 >
 >
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 --
 Mariusz Radon, PhD student
 Department of Theoretical Chemistry
 Jagiellonian University
 http://www.chemia.uj.edu.pl/~mradon
 mradon /at/ chemia.uj.edu.pl
 (PGP public key available on the website)
 --
 Mariusz Radon, PhD student
 Department of Theoretical Chemistry
 Jagiellonian University
 http://www.chemia.uj.edu.pl/~mradon
 mradon /at/ chemia.uj.edu.pl
 (PGP public key available on the website)