Doing frequencies calculations: frequencies
Using the executable frequencies, it is possible to calculate the vibrational properties of a system by finite difference. The atomic system is moving for each direction and each atom in a small step in order to calculate the Hessian matrix by a finite difference scheme. A checkpoint restart is implemented. The file ’frequencies.res’ contains the previous calculations.
It uses an additional input file.
Three files are created:
- ’frequencies.xyz’ containes the eigenmodes visualizable directly using v_sim;
- ’hessian.dat’ contains the Hessian matrix and;
- ’dynamical.dat’ contains the dynamical matrix i.e. the weighted mass Hessian matrix.
It is possible to move only certain atoms if in the atomic position file some atoms are specified as frozen (see Atomic positions file format).
To find quickly in the output file, the lines associated to the frequency calculations use as command:
- grep '(F)' output_file