In routine work on my beamline, Vesuvio, at the ISIS spallation source, I have to model neutron transmission and the neutron Compton-scattering spectra using the same underlying atom-projected VDOSes, Z_M(\omega), where M is the mass of an isotopic species.
The neutron transmission (total cross-section) simulations seem to work well within the existing NCRYSTAL computational framework and syntax, whereby one uses a global (thermodynamic) temperature parameter next to the specification of the .ncmat file.
However, the neutron Compton scattering simulations, to work, need to have one effective temperature, T*, per isotopic species. This effective temperature can be calculated as:
T* = \int d\omega \omega Z_M(\omega) coth[\hbar \omega/(2k_BT)] [Eq. 1]
I am attaching a recent publication demonstrating this challenge. In the attached paper, the transmission was calculated using NCYSTAL, while the Compton spectra and atomic displacement parameters for the interpretation of the diffraction data were modelled with bespoke codes. The momentum distributions were assumed to have Gaussian underlying momentum distributions with widths \sigma calculated using:
\sigma = 3/4 \int d\omega \hbar \omega Z_M(\omega) coth[\omega/(2k_BT)] [Eq. 2]
Thus, there is a relation between T* and sigma:
k_B T*/2 = \hbar^2 \sigma^2 / (2 M) [Eq. 3]
Krzystyniak_2023_Phys._Scr._98_025707.pdf
Krzystyniak_2023_Phys._Scr._98_025707_SI.pdf
I am also attaching a link to the shared OneDrive directory containing the original data and models:
https://1drv.ms/f/c/8668037d24089571/IgBxlQgkfQNoIICGNdYCAAAAAf9ih2XcnKeg4etpjeNL71M?e=VYb4Jf
In routine work on my beamline, Vesuvio, at the ISIS spallation source, I have to model neutron transmission and the neutron Compton-scattering spectra using the same underlying atom-projected VDOSes, Z_M(\omega), where M is the mass of an isotopic species.
The neutron transmission (total cross-section) simulations seem to work well within the existing NCRYSTAL computational framework and syntax, whereby one uses a global (thermodynamic) temperature parameter next to the specification of the .ncmat file.
However, the neutron Compton scattering simulations, to work, need to have one effective temperature, T*, per isotopic species. This effective temperature can be calculated as:
T* = \int d\omega \omega Z_M(\omega) coth[\hbar \omega/(2k_BT)] [Eq. 1]
I am attaching a recent publication demonstrating this challenge. In the attached paper, the transmission was calculated using NCYSTAL, while the Compton spectra and atomic displacement parameters for the interpretation of the diffraction data were modelled with bespoke codes. The momentum distributions were assumed to have Gaussian underlying momentum distributions with widths \sigma calculated using:
\sigma = 3/4 \int d\omega \hbar \omega Z_M(\omega) coth[\omega/(2k_BT)] [Eq. 2]
Thus, there is a relation between T* and sigma:
k_B T*/2 = \hbar^2 \sigma^2 / (2 M) [Eq. 3]
Krzystyniak_2023_Phys._Scr._98_025707.pdf
Krzystyniak_2023_Phys._Scr._98_025707_SI.pdf
I am also attaching a link to the shared OneDrive directory containing the original data and models:
https://1drv.ms/f/c/8668037d24089571/IgBxlQgkfQNoIICGNdYCAAAAAf9ih2XcnKeg4etpjeNL71M?e=VYb4Jf