multiphonon

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.

Features

• 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 (requires Mantid)

Development Installation and Testing

Create and activate a virtual environment with Pixi.Prerequisites: Pixi installation e.g. for Linux:

curl -fsSL https://pixi.sh/install.sh | sh

Download the repository. Setup/Update the environment

pixi install

Enter the environment

pixi shell

```bash See "Run test" section below for how to set up git-lfs and run unit tests

```

Installation

Installation is handled with conda. Please see Installation instructions for details.

Usage

Please see usage for details.

Community guidelines

How to contribute

Please clone the repository, make changes and make a pull request.

How to report issues

Please use the github issues to report issues or bug reports.

Support

Please either use the github issues to ask for support, or contact the authors directly using email.

Algorithm

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].

API doc

See https://multiphonon.readthedocs.io/en/latest/api.html

(previous http://neutrons.github.io/multiphonon/api.html)

Run tests

Tests are run automatically at CI

Due to certain test files exceed github storage limit, git-lfs(large file storage) has been set up to host these test data. Git-lfs will need to be configured on local machine to download test data. To set up git-lfs, in root folder "multiphonon/" run:

$ git lfs pull
$ git submodule update --init --recursive

A folder named "multiphonon-data" should appear under "tests/data/", from here run: $ pixi shell $ pytest

to run all tests or follow instructions below to run minimal tests .

To manually run the minimal test suite, install multiphonon, clone this repository, and run

$ cd multiphonon/tests && py.test -m "not needs_mantid and not needs_ipywe"

If mantid and ipywe were installed, you can run all tests by

$ py.test

References

[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

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