Molecular one‐electron properties using the multireference Hartree–Fock CI method

Abstract

ABSTRACT:The recently introduced multireference Hartree-Fock configuration interaction (MRHFCI) method has been applied to the calculation of the dipole moment of the LiH, BH, FH, CO, and H 2 O molecules. The results obtained indicate that MRHFCI wave functions, much more compact but of the same quality of the orthogonal full CI ones, can provide better dipole moments than the corresponding full CI wave functions. The value of the dipole moments obtained with the MRHFCI wave functions is quite insensitive to the choice of the HF references but the same is not true for the electronic energy. Therefore, further studies are necessary to develop a criterion for selecting a set of HF references which could provide the best values of energy and dipole moment. Also, it would be important to verify if other one-electron properties can be computed with the same degree of accuracy obtained for the dipole moments.

Quadrupole moment of the hydrogen fluoride using the multireference Hartree–Fock CI method

“…It would be interesting to verify the possibility of obtaining, with reduced MRHF bases, good results for the one‐electron properties using larger atomic bases and/or property‐optimized bases sets. This possibility has been corroborated in a previous study4 in the calculation of the dipole moment of the LiH molecule using the STO‐6G, CFG‐6G, DZ, TZ, and DZ p bases. In those calculations, it was observed a decline with the increase of the atomic basis, in the ratio between the dimensions of the MRHF and full CI bases.…”

“…This possibility was tested in previous works,3, 4 where we investigated the permanent electrical dipole moment of some AH molecules, using the MRHFCI method and the standard STO‐6G bases and a new minimal basis CFG‐6G 6. In all cases, we have obtained electrical dipole moments close to the experimental results with a reduced number of configurations in the MRHF basis.…”

“…Similarly to Ref. 4, Tables 1 and 2 are organized in the following way: the first column is just a number to identify the different calculations performed for the system; the second and third columns indicate the total number of CSFs and the energy of the Hartree–Fock references (labeled by capital letters) used in the MRHFCI calculation, respectively; the fourth and fifth columns show the values of MRHFCI energy and dipole moment; the sixth column shows the component Q zz of the quadrupole moment traceless matrix. The last row contains the same results of the orthogonal full CI calculation for the system.…”

“…Multireference configuration interaction (MRCI) methods have been developed and used in molecular quantum mechanics 1, 2. In previous works,3, 4 we have introduced a new MRCI method, based on the multiple solutions of the Hartree–Fock problem,5 called the multireference Hartree–Fock configuration interaction (MRHFCI) method. In the MRHFCI method, instead of a single reference—the Hartree–Fock fundamental state, one uses several Hartree–Fock extremes as references to expand the state function.…”