Manual:oct-vibrational

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This utility calculates the vibrational spectrum from a molecular dynamics run.

What this utility does is to read the velocity from the td.general/coordinates and calculate the Velocity Autocorrelation Function:

C_{v}(t)=\sum_{i=1}^{N_{atoms}}\vec{v}_i(t)\cdot\vec{v}_i(t_0)\ ,

afterward a cosinusoidal evelope is added, to make the periodic extension of the function continuous and then the spectrum is calculated by taking the fourier of the function. On exit two files are generated td.general/velocity_autocorrelation and td.general/vibrational.

This utility honours the variables SpecStartTime and SpecEndTime to control the time of sampling. Note that the veloctiy in the initial time must be different from zero, or Cv will be identically zero.

As a discrete fourier tranform is used, this utility can take several minutes to process a large run. If Octopus was compiled with OpenMP support this utility can run in several threads.

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