Subject: How to calculate excitation energy in high accuracy by Gaussian?

From: "Kiniu WONG Kin-Yiu" <[email-masked]>
Date: Sun, 1 Oct 2000 20:26:35 +0800

Hi all,

    I couldn't get an accurate excitation energy by Gaussian, even a simple
atom such as Hydrogen and
Beryllium. The excitation energy of H is 10.2eV, but by
UCIS(50-50)/6-31+G(d), it gives the excitation energy = 26.1eV:

 CIS wavefunction symmetry could not be determined.
 Excited State   1:   ?Spin  -?Sym   26.1001 eV   47.50 nm  f=0.0000
      1A ->  2A        1.00000
 This state for optimization and/or second-order correction.
 Total Energy, E(Cis) =   .460934644427

The excitation energy of Be is 2.7eV, but by UCIS(50-50)/6-31+G(d), the
excitation energy = 1.69eV:

 CIS wavefunction symmetry could not be determined.
 Excited State   1:   Triplet-?Sym    1.6892 eV  733.98 nm  f=0.0000
      2A ->  3A         .47494
      2A ->  5A         .15415
      2A ->  7A        -.26459
      2A ->  9A         .40156
      2B ->  3B        -.47494
      2B ->  5B        -.15415
      2B ->  7B         .26459
      2B ->  9B        -.40156
 This state for optimization and/or second-order correction.
 Total Energy, E(Cis) =  -14.5076545141

What's wrong? Have I made some mistakes?

    Thanks for any help in advance!

Regards,
Kiniu

------
Kiniu WONG Kin-Yiu
Undergraduate student
Department of Physics
The Chinese University of Hong Kong
Email: [email-masked]  or  [email-masked]