[Octopus-users] about casida

[Hongjun Xiang]

Dear all,
  I tried to calculate the optical spectra using the Casida method.
I found that the first excitation energy is lower than the LDA Kohn-Sham
HOMO-LUMO gap.
Is this meaningful within the TDLDA theory or it just indicates problems in
the computation setting?

Thank you.

Best regards,
Hongjun Xiang

=============================================================
H. J. Xiang
Postdoctoral Research Associate
National Renewable Energy Laboratory
http://www4.ncsu.edu/~hxiang/
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