Computation of electronic molecular polarizabilities by a variational method at the CISD level

✍ Scribed by Alain Cartier; Marilia T. C. Martins-Costa; Daniel Rinaldi

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 722 KB
• Volume: 60
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1996)60:4<883::aid-qua11>3.0.co;2-6

✦ Synopsis

The variational method proposed earlier has been generalized, using a trial function of the form: I) = (A, + Cshsm,)I)o in which m, = r2P+'C?, s standing for a triplet ( p , I , m ) and implemented into the program Hondo-8.4. The second-order density matrices are used to take into account the mono and bi-excited states (DM1 and Dh42 matrices, GUGA Algorithm). This allows us to compute the dipole (a), dipole-quadrupole (A) and quadrupole (C) polarizability tensors at the CISD level. The results obtained for a series of test molecules: CO, HF, NH,, and methane with various gaussian basis sets are compared with experimental results (when available for A and C) and those obtained with other theoretical methods. The correlation is found to lower the values of the dipole polarizability which was generally too high when computed by the variational method at the RHF level and the values obtained here are in good agreement with the experimental ones. 0 1996 John Wiley & Sons, Inc. fields used in molecular mechanics computations are usually based on the assumption that the interaction between nonbonded atoms can be analyzed in the same way as iritermolecular interactions. Therefore, a possible improvement of modern force fields is expected from the introduction of a n induction term [Z-61. Unfortunately accurate experimental data on the electronic polarizabilities of ested in the whole tensorial quantity instead of the