On the theory of non-adiabatic effects in molecules

✍ Scribed by E. Deumens; L. Lathouwers; P. Van Leuven

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 354 KB
• Volume: 112
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(84)85754-1

✦ Synopsis

It is shown that the generator coordinate approximation introduces non-adiabatic effects of the correct sign (ener,g lowerinrz) and size (Born-Oppenheimer analysis)_ The theoretical expression applied to diatomic molecules qualitatively explains the observed trends of non-adiabatic energy corrections both in the adiabatic retion of the spectrum and in the region of avoided crossings.

The traditional way to go beyond the Born-Oppenheimer and adiabatic approximations is to expand the total molecular wavefunction in the complete set of electronic eigenstates. In this approach, due to Born and Huang [I], non-adiabatic correlation between electronic and nuclear motion is introduced through coupling of different electronic eigenstates. Recently we proposed the generator coordinate approximation (GCA) [2] in which nonadiabatic effects are derived from a single electronic state. In this sense the new method is similar to the adiabatic approximation (AA). However, whereas the adiabatic wavefunctions are simple products, \kAU(r, R) = q(rlR) X FAD(R), the GCA trial states are of the form * Research supported by the NSF (USA) and the NFWO (Belgium).