Transferability of Urey-Bradley Force Constants. I. Calculation of Force Constants on a Digital Computer

An algorithm for the systematic calculation of Urey-Bradley force constants has been programed for a digital computer (the Datatron 204). The secular equation is set up and solved in internal coordinates, the potential energy being transformed from Urey-Bradley space to internal-coordinate space by a matrix Z. This same matrix is also used to transform the Jacobian of λ with respect to the force constants from internal-coordinate to Urey-Bradley space, thereby allowing the direct determination of Urey-Bradley force constants. A method is described whereby the Z matrix and Wilson's G matrix may be set up by the computer from the geometrical parameters of the molecule.