# Difference between revisions of "Manual:External utilities:oct-vibrational spectrum"

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afterward a cosinusoidal envelope is added, to make the periodic extension of the function continuous and then the spectrum is calculated by taking the Fourier transform of the function. On exit, two files are generated {{file|td.general/velocity_autocorrelation}} and {{file|td.general/vibrational}}. | afterward a cosinusoidal envelope is added, to make the periodic extension of the function continuous and then the spectrum is calculated by taking the Fourier transform of the function. On exit, two files are generated {{file|td.general/velocity_autocorrelation}} and {{file|td.general/vibrational}}. | ||

− | This utility honours the variables {{Variable| | + | This utility honours the variables {{Variable|PropagationSpectrumStartTime|Utilities}} and {{Variable|PropagationSpectrumEndTime|Utilities}} to control the time of sampling. Note that the velocity in the initial time must be different from zero, or <math>C_{v}</math> 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. | 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. | ||

{{manual_foot|prev=Manual:External utilities:oct-vdW_c6|next=Manual:External utilities:oct-xyz-anim}} | {{manual_foot|prev=Manual:External utilities:oct-vdW_c6|next=Manual:External utilities:oct-xyz-anim}} |

## Latest revision as of 13:42, 7 September 2016

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:

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

**.**

`td.general/vibrational`This utility honours the variables `PropagationSpectrumStartTime`

and `PropagationSpectrumEndTime`

to control the time of sampling. Note that the velocity in the initial time must be different from zero, or 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.