[molpro-user] Unclear problem in EOM-CCSD calculations: "small eigenvalue of S-eff matrix ... This can lead to convergence problems!"
tania at tiger.chem.uw.edu.pl
Mon Jul 10 12:05:46 CEST 2017
I have investigated this case. It turns out that we have a rare case that the
two lowest eigenvalues are complex (i.e. their real part is the lowest :-) ).
Usually such situations appear for much higher states. Probably I have to add a
special information and to stop the calculation in the subroutine controlling
the Davidson convergence.
With the production version you can see this if you add extended eomprint
eomprint,davidson=4,residual=4 ! maybe this is a bit too much of printing
and look at the string "and after reordering". Below there will be the
eigenvalues with real and imaginary parts listed separately. You will see that
from some moment you will have a small (plus/minus 0.1e-3) imaginary part.
The possible existence of complex eigenvalues is a side effect of the
nonsymmetric similarity-transformed Hamiltonian exp(-T)Hexp(T), so it is the
feature, not the error.
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
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