VT relaxation time computation

Python code to compute VT relaxation times using a kinetic theory based definition, as developed in Kustova, E. V., and G. P. Oblapenko. "Mutual effect of vibrational relaxation and chemical reactions in viscous multitemperature flows." Physical Review E, 2016 and G. P. Oblapenko. "Calculation of Vibrational Relaxation Times Using a Kinetic Theory Approach." The Journal of Physical Chemistry A, 2018.

More specifically, it computes the either the averaging operator over all possible one-quantum VT transitions using the Forced Harmonic Oscillator model and the Variable Soft Sphere model with recent collision parameters to calculate the transition cross-sections.

The code can compute either the averaging operator avg_E_vibr, or the full relaxation time t (at a specified pressure), defined as

t = m * c_vibr / (4 * k * n * avg_E_vibr),

where m is the relaxating molecules mass, k is the Boltzmann constant, n is the number density, c_vibr is the specific heat of vibrational degrees of freedom.

Usage

The code requires Python 3, the netCDF4 library, numpy and scipy.

To install the pre-requisites:

pip install numpy

pip install scipy

pip install netCDF4

Another option is to use the Anaconda distribution, and install netCDF4 via conda install netcdf4.

The script can be run with the following optional arguments:

optional arguments:

• -h, --help: show this help message and exit
• -t OUTPUTFILETYPE, --outputfiletype OUTPUTFILETYPE specifies output filetype: CSV or NETCDF4 (default is "NETCDF4")
• -f OUTPUTFILENAME, --outputfilename OUTPUTFILENAME specifies output filename (or prefix in case of CSV files, a separate CSV file is created for each interaction pair)
• --cdfoutputfileformat CDFOUTPUTFILEFORMAT For netCDF4 output, specifies output format (default is "NETCDF4_CLASSIC")
• --delimiter DELIMITER For CSV output, specifies delimiter (default is ",")
• --molecules MOLECULES Comma-separated names of molecules for which the VT relaxation times are computed (default is "N2,O2,NO")
• --partners PARTNERS Comma-separated names of particles, possible collision partners (default is "N2,O2,NO,N,O,Ar")
• --temperaturemin TEMPERATUREMIN Minimum temperature (default is 200.0)
• --temperaturemax TEMPERATUREMAX Maximum temperature (default is 25000.0)
• --vtemperaturemin VTEMPERATUREMIN Minimum vibrational temperature (default is 200.0)
• --vtemperaturemax VTEMPERATUREMAX Maximum vibrational temperature (default is 25000.0)
• --dt DT Temperature step size (default is 100.0)
• --verbose VERBOSE If set to true (default value), will enable some output during computation
• --integral_only INTEGRAL_ONLY If set to true (default value), will compute only averaging operator and not the full relaxation time
• --pressure PRESSURE If integral_only is not true, this will specify the pressure in Pascals at which the relaxation times are computed (default is 101325 Pa)

Citing

Oblapenko, G. P. Calculation of Vibrational Relaxation Times Using a Kinetic Theory Approach. The Journal of Physical Chemistry A, 2018. http://doi.org/10.1021/acs.jpca.8b09897

Kustova, E. V., and G. P. Oblapenko. Mutual effect of vibrational relaxation and chemical reactions in viscous multitemperature flows. Physical Review E, 2016. https://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.033127