Calculation of Vibrational Wavenumbers of Octahedral Closed-Shell Complexes Using Semiempirical Methods of Quantum Chemistry

Quantum-chemical computations for systems con­ taining heavier atoms meet troubles of two kinds at least. The first one concerns the systems contain­ ing transition metal atoms. In such cases, one needs to use extraordinary extensive basis sets for obtain­ ing reliable results. Therefore, at present one can­ not expect a common use of ab initio computations in the area of solving of object-oriented problems in which transition metal atoms occur. The second trou­ ble follows from the requirement to include relativistic effects in the case of heavier atoms. The use of a semiempirical quasirelativistic method consistently parametrized for a wide range of elements offers an acceptable solution of these troubles. Quasi-rela­ tivistic INDO/1 (QR-INDO/1) method [1] meets these requirements. With regard to the known drawbacks of the ZDO-type methods this paper is devoted to the testing of the ability of QR-INDO/1 to provide a correct description of curvature of energy hypersurface in the vicinity of its minima. Usually, the ZDOtype methods are not very successful at this task. For obtaining of reliable frequencies, the scaling of the force constants computed using ZDO methods very often must be applied. The next motivation and future application of this work follows from the need to identify some complexes generated by electro­ chemical processes in molten salts [2].