Cartesian Atomic Forces from File
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Dialog Box: Cartesian Forces from File [Control window: Forces menu]

VIBRATZ can use either valence forces, or Cartesian atomic forces. If one of the Use Cartesian forces radio buttons is checked, a matrix of Cartesian atomic forces is read in, and any forces entered in the dialogs of the Forces menu are ignored. This matrix must contain x, y and z entries for each atom listed in the "All Atoms in Unit-Cell/Molecule" section of the output; that is, all atoms, not just a symmetry-unique set, must be included. The matrix should be in lower-diagonal form, and the number of entries per line in the file is not important. The total number of entries should be 3n*(3n+1)/2.

The Raman intensities are based entirely on changes in bond lengths using the bond polarizabilities assigned in the Bonds dialog (Forces menu). Thus the Use Cartesian forces with bonds radio button must be selected if Raman intensities are to be calculated, and appropriate bonds must be defined in the Bonds dialog of the Forces menu. The force constants entered for bonds are ignored in this case, i.e. the bond forces are not used at all.

Factor to apply. This multiplies every element of the Cartesian force matrix prior to the calculation. If the Cartesian matrix is in units other than md/A, this can be the scaling factor (e.g. 15.56914 to convert from Hartrees/Bohr^2). If the Cartesian matrix is from a molecular orbital calculation (e.g. GAUSSIAN) there may be an overall bias, which can be counteracted with this factor.

The scale factor will be refined in a Calculation by the step-by-step least-squares method if any least-squares option is chosen when one of the Use Cartesian Forces option is selected in this dialog. This is all that will be refined in that case. Of course you must have observed frequencies to do this.