Neutron spectroscopy
Measures the atomic and magnetic motions of atoms.
Inelastic neutron scattering measures the change in the energy of the neutron as it scatters from a sample. This can be used to probe a wide variety of different physical phenomenon: diffusional or hopping motions of atoms, the rotational modes of molecules, sound modes and molecular vibrations, recoil in quantum fluids, magnetic and quantum excitations or even electronic transitions.
Often knowing the atomic structure of a material will be sufficient to understand its nature. But to gain a deeper insight into the underlying physics of say a phase change, it is necessary to also understand the atomic dynamics. The vibrational motion of atoms is, entirely or in part, responsible for a large number of the characteristic properties of a material, such as the specific heat, thermal conductivity, optical and dielectric properties and electrical resistance, but it is also a direct way of understanding the nature of atomic bonding. And with the current interest in smart or functional materials whose properties are often determined by a complex balance or strong coupling between competing phenomena, understanding the atomic and magnetic dynamics is essential.
The most commonly used spectroscopies are the light scattering techniques: Raman and infrared. Compared to neutron scattering they are cheap, readily available and highly sensitive. But they do have certain limitations: They can only measure near the Brillouin zone centre and are only sensitive to certain vibrational modes. The calculation of the scattered intensity is also difficult and prone to error and so information is usually only taken from the positions of the observed modes. However, the simplicity and sensitivity of the techniques means that they are often used to identify or ‘finger print’ compounds something that is rarely done with neutrons. Inelastic neutron scattering is usually used to understand the physics of a system. It is a highly quantitative probe whose results are directly comparable to numerical and analytical calculation.
It can be used to understand the nature of a phase transitions or linked directly to thermodynamics quantities, like specific heat or thermal conductivity, or structural properties such as force tensors or bulk and shear moduli. It is still one of the few methods available to measure phonon and magnon dispersion curves. And, due to the unique nature in way that hydrogen scatters neutrons, it is a natural technique for measuring the vibration or diffusion of hydrogen in a material.
Neutron spectroscopy data analysis
Molecular Dynamics Analysis of Neutron Scattering Experiments (MDANSE)
Inelastic and quasi-elastic neutron scattering (INS and QENS, respectively) spectroscopy are useful tools for probing molecular dynamics in materials. Atomistic simulations, particularly molecular dynamics (MD) simulations are being used increasingly for analysis of these data. However, predicting neutron observables from MD trajectories is not straightforward. A number of operations, such as calculations of velocity auto- and cross-correlation functions, Fourier transformations and convolutions with instrument parameters are required to calculate neutron observables that can be compared directly with experimental data.
Some of these steps were implemented in the open source MDANSE (Molecular Dynamics Analysis of Neutron Scattering Experiments). This software has interface with more than ten MD codes including some ab-initio MD codes, such as CASTEP, VASP, DMOL, Gromacs, etc. showing potential to be used widely.
In the current project, we have taken the initiative to upgrade the MDANSE code so that it would be easy to use and compile, written in python3 and dependencies transferred from NetCDF to HDF in addition to reducing dependencies on some old software, such as Pyro. Individual scripts from this developed utility can be accessed by users for their particular use without using the full code.
The sustainable software and utility will be an asset to the future neutron scattering community for atomistic simulations and neutron scattering data analysis.
Downloads
From the release MDANSE 2.0.0 the code is written fully on python 3 and free from any dependencies on unsustainable software. The MDANSE GUI package is separated from MDANSE 2, which can be run in scripting mode. The beta version of the new build can be downloaded from below. Users are requested to provide feedback and report any bugs to MDANSE development team.
Installing MDANSE — MDANSE 2.0.0b1 documentation
(Last updated September, 2025)
ab-initio interpretation of Inelastic Neutron Scattering Spectroscopy (abINS)
Inelastic neutron scattering (INS) spectroscopy provides a richer microscopic insight into a material due to the absence of structural symmetry related selection rules generally observed in other vibrational spectroscopies, such as in infrared and Raman spectroscopies.
INS depends on both energy (E) and momentum (Q) transfer of neutrons due to interaction of lattice phonon providing further microscopic details of interatomic interactions. First-principles density functional theory (DFT) based simulations can be used to calculate vibrational frequencies and phonon dispersion relations. However, results of such calculations are not directly comparable with experimental INS spectra. There is a need to include the neutron scattering cross sections, overtones and combination modes, together with instrument resolutions and specific E-Q windows.
AbINS algorithm is a tool, which resides in the open-source Mantid framework bringing simulation to the same environment as experimental reduction and analysis, includes efficient calculation of multi-phonon spectra and supports a variety of instruments and simulations software including Phonopy. This graphical users interface (GUI) based application uses the normal modes from DFT calculations and it is straightforward to interpret experimental INS with simulations.
Two tools are available to interpret vibrational spectroscopy and phonon dispersions available from indirect geometry and direct geometry neutron instruments, called abINS and abINS2D, respectively. The following features are available in these tools:
ABINS for vibrational spectroscopy:
- calculate structure factor S(Q,w) from DFT lattice dynamics data
- interface with a number of DFT lattice dynamics packages: CASTEP, CRYSTAL, DMOL3, GAUSSIAN, VASP, PHONOPY
- temperature corrections available through the Debye-Waller factor and Bose populations analysis.
- control over overtones (1 to 10)
- atom projected INS spectrum for in-depth analysis
- convolution with number of instrument parameters, such as TOSCA, LAGRANGE,
More information about abINS can be found here.
ABINS-2D for phonon dispersion:
- calculate structure factor S(Q,w) from DFT lattice dynamics data
- interface with a number of DFT lattice dynamics packages: CASTEP, CRYSTAL, DMOL3, GAUSSIAN, VASP, PHONOPY
- temperature corrections available through the Debye-Waller factor and Bose populations analysis.
- control over overtones (1 to 10)
- atom projected INS spectrum for in-depth analysis
- convolution with number of instrument parameters, such as MAPS, MARI, MERLIN, PANTHER,
- instrument parameters are applied through incident energies and chopper settings
- geometry limits and resolutions are applied automatically
More information about abINS-2D can be found here.
Download Mantid to use these tools.
If you use abINS, please cite:
K Dymkowski, SF Parker, F Fernandez-Alonso and S Mukhopadhyay, “AbINS: The modern software for INS interpretation”, Phys. B 551, 443 (2018). doi:10.1016/j.physb.2018.02.034
To know more about the project and discuss your requirements from the software contact Sanghamitra Mukhopadhyay.