This is a rewrite of multiphonon (getDOS) code that was originally authored by Max Kresch during the DANSE project and was then revised by several authors including Brandon, Chen, Jennifer, and Dipanshu (their work were recorded as branches in this repo). It fixes some problems in the earlier versions of getDOS code and implemented new features. The original requirements of this project is captured at this ticket. And details of the features of this code can be found below.
Main functionality: Compute phonon Density of States (DOS) from powder Inelastic Neutron Scattering (INS) spectrum
Inelastic neutron scattering (INS) are important probes of dynamics in materials [2]. Powder spectra measured by inelastic neutron spectrometers provide information such as phonon density of states (DOS), a fundamental property of a solid. The measured spectra, however, are two-dimensional in axes of Q (momentum transfer) and E (energy transfer). This code converts a S(Q,E) INS spectrum to DOS.
- The full I(Q,E) dynamic range measured is utilized, leading to better statistics
- Can be used with data measured at multiple incident energies to progressivley obtain better density of states
- Intermediate results are saved for further investigation
- Handle inputs in nxs and nxspe files for sample and empty can measurements
NOTE: SNS users can skip this step and use this software package directly at SNS analysis cluster (see below).
The multiphonon package can be installed using conda (python 2) on a recent 64bit linux (ubuntu/fedora/centos) distribution:
$ conda config --add channels conda-forge
$ conda config --add channels mantid
$ conda config --add channels mcvine
$ conda config --add channels neutrons
$ conda install numpy
$ conda install multiphonon
Information on dependencies of this code can be found at the conda recipe
For SNS users, GetDOS can be performed at SNS analysis cluster through the jupyter.sns.gov website.
- First log into SNS analysis cluster using thinlinc. The instructions for that can be found at https://analysis.sns.gov/
- Inside the thinlinc session of analysis.sns.gov, open a browser window and connect to https://jupyter.sns.gov, and login with your XCAMS/UCAMS account credentials
- Follow the tutorial videos below:
- For the first time users, a setup is necessary
- Run GetDOS2 (this works for SNS data only)
For any user, GetDOS can be performed with a local installation of GetDOS and jupyter. Examples and instructions can be found here
The core algorithm is an iterative procedure:
- Start with the input SQE and an initial guess of DOS
- Calculate SQE of multiphonon scattering (MP)
- Calculate SQE of multiple scattering (MS) using C_ms and multiphonon scattering SQE
- Subtract MS and MP SQE from the experimental SQE to obtain an approximation of the single-phonon SQE
- Compute a new DOS from the single-phonon SQE
- Compare the new DOS to the initial guess and calculate the difference
- If difference is large, continue the iteration using the new DOS as the initial guess. Otherwise, output the new DOS and stop iteration
For more details of the basic principles of SQE->DOS conversion, please refer to Appendix of [1] and Section 6.5 "Calculation of Multiphonon Scattering" of [2].
See http://sns-chops.github.io/multiphonon/
[1] Max Kresch et al., https://journals.aps.org/prb/abstract/10.1103/PhysRevB.75.104301
[2] Brent Fultz et al., http://www.cacr.caltech.edu/projects/danse/doc/Inelastic_Book.pdf