V2 - Vibrations => calculation [normal modes]

Here it is possible to calculate the phonon frequencies and the normal modes for every representation of the group. The V2-menu initially looks as follows:

>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<

MOLECULE: lattice translations IGNORED

========= CHOOSE an OPTION:

FE. Current working algorithm: via Forces

-------- E x i s t i n g -- I r r e p s --------

1. irrep (A1 ) is 1D; dim = 2; G-files[ T], F_files[ T] W-files[ T]

--- A c t i o n s w i t h A c t i v e I r r e p -----

-------- G e n e r a l S e t t i n g s --------

XY. Format of <movie.xyz> file is for Xmol

Hs. H atoms to be added to <movie.xyz> file: NO

Da. Distortion amplitude for movies: 0.05000

Q. Proceed/Quit

-----> Choose an appropriate option:

The fist line reminds the user which option (Vm, Vc or Vs of the main menu) was used to generate the distirted geometries. In the example above, this was Vm.

If any of the existing representations are displayed under ``Existing Irreps'', then all the necessary files exist and were read in successfully (including the forces on atoms calculated by running the run_DFT_script for distorted geometries). Otherwise, they will not be shown. At least one representation should be available to proceed.

Then, choose the representation number, 1 in the example above (A1). The dynamical matrix for this representation will be diagonalised and the corresponding eigenvalues and eigenvectors calculated. The precision of the calculation is checked and, if the relative difference between nondiagonal elements of the FCM is large, an warning will be given^2.2. The menu changes into:

>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<

MOLECULE: lattice translations IGNORED

========= CHOOSE an OPTION:

FE. Current working algorithm: via Forces

-------- E x i s t i n g -- I r r e p s --------

1. irrep (A1) is 1D; dim = 2; G-files[T], F_files[T] W-files[T] <=== now active

--- A c t i o n s w i t h A c t i v e I r r e p -----

Sv. Show eigenvalues/vectors

Sa. Show frequencies and normal modes

Vs. Write xyz movie file for each mode

-------- G e n e r a l S e t t i n g s --------

XY. Format of <movie.xyz> file is for Xmol

Hs. H atoms to be added to <movie.xyz> file: NO

Da. Distortion amplitude for movies: 0.05000

Q. Proceed/Quit

-----> Choose an appropriate option:

Three new options appeared:

• Sv - shows the calculated eigenvalues (the squares of frequencies in inconvenient units) and eigenvectors (with respect to the symmetry adapted displacements); the displayed information is not very useful and may only be needed for an advance user; a file EIGEN_1.res will be written with the identical information;
• Sa - this gives all phonon frequencies (in cm$^{-1}$) and normal coordinates; the latter are given in terms of atomic diaplcements; a file N_MODES_1.res will be written with identical information;
• Vs - each normal coordinate can be run sinusoidally, written into a movie file movie.xyz (controlled by options Hs, Da and XY) and then previewed with the Xmol or similar molecular viewer.