[molpro-user] Unclear problem in EOM-CCSD calculations: "small eigenvalue of S-eff matrix ... This can lead to convergence problems!"
evgeniy.gromov at pci.uni-heidelberg.de
Wed Jun 21 11:34:04 CEST 2017
Many thanks for your response. While struggling with the problem I
increased the integral accuracy (to 1dE-20) as well as
the accuracy for the T1+T2 amplitudes (to 1dE-12) . However, this did
not help. Concerning the Davidson, the default
20 vectors per state should be OK because the problematic state is
actually the lowest one. It is in fact a doubly degenerate (E')
state, that is there are two states of A' (the molecule has C3h
symmetry, the computational group is Cs).
I do not think the problem relates to degeneracy, as other, higher-lying
degenerate states converge smoothly.
The problem occurs only at the EOM-CCSD level, at ADC(2) everything is
fine. I also tried EOM in CFOUR and it is
the same. I am stumped with what can be wrong with that state.
I wonder what one could look at (print out) to trace the problem back?
On 06/07/2017 05:20 PM, Tatiana Korona wrote:
> Dear Evgeniy,
> This message can signify near-linear dependencies in the small space
> in the Davidson procedure. One can try to a) increase the quality of
> the integrals (for the case when this dependence is caused by
> numerical noise of orbitals and CCSD amplitudes - note that if CCSD is
> not a final step, a bit more accurate T1+T2 amplitudes are often
> required); b) try to play with Davidson options, e.g. change MAXDAV.
> Another issue is a high energy of the virtual orbital. I presume you
> want to obtain some high-lying states, what often means that there is
> a large density of states having a significant component of the
> excitation to this orbital and then the procedure will jump from one
> state to another and back (or to yet another state). In this case
> sometimes it helps if you ask for more states (but only sometimes). In
> general finding high states is a difficult no-black-box task,
> unfortunately :-(
> Best wishes,
> On Tue, 6 Jun 2017, Evgeniy Gromov wrote:
>> I encountered some unclear problem when doing EOM-CCSD calculations
>> for an Ir complex. All steps till EOM went fine, but in EOM I get the
>> following warning:
>> The smallest eigenvalue of S-eff matrix 0.8656157915E-13
>> This can lead to convergence problems!
>> and two of the five roots do not seem to have converged; there is
>> no "Converged" message for them after 50 iterations.
>> I wonder what this could be caused by? Could it be due to a very high
>> in energy (63.5 hartree) virtual orbital?
>> Best regards,
>> Dr. Evgeniy Gromov
>> Theoretische Chemie
>> Physikalisch-Chemisches Institut
>> Im Neuenheimer Feld 229
>> D-69120 Heidelberg
>> Telefon: +49/(0)6221/545213
>> Fax: +49/(0)6221/545221
>> E-mail: evgeniy.gromov at pci.uni-heidelberg.de
>> Molpro-user mailing list
>> Molpro-user at molpro.net
> Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/index.html
> Quantum Chemistry Laboratory, University of Warsaw, Pasteura 1,
> PL-02-093 Warsaw, POLAND
Dr. Evgeniy Gromov
Im Neuenheimer Feld 229
E-mail:evgeniy.gromov at pci.uni-heidelberg.de
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