Knowledge Bank

The formalism of the Block Triangular Matrices is used to develop the High and Low Frequency Separation Method (HLFS). It can be shown that a. complete set of ""pseudo-exact"" force constants can be set up from the solutions of the two truncated secular equations corresponding respectively to the high and low frequencies. Moreover, the theory of HLFS is extended to other molecular constants (say, compliances, Coriolis coupling constants, mean square amplitudes); then, relations connecting the molecular constants of each truncated block are seen to be useful in the search of the solution of the corresponding secular equation when additional data are known.