MedeA Phonon - Vibrational Spectra, Thermal Behavior, and Phase Stability

At-a-Glance

MedeA®[1] Phonon is an essential tool for researchers interested in the behavior of solids, surfaces, interfaces, and molecules at finite temperatures. In solids, MedeA Phonon computes collective atomic vibrations (phonons) to determine the free energy, which in turn allows you to predict properties like heat capacity and phase stability. By visualizing and animating the collective atomic vibrations, you can identify atomic motions that lead to reactions and phase transitions. Moreover, simulations of IR and Raman spectra allow a detailed understanding of the vibrational modes responsible for spectral features.

Key Benefits

  • Predict material behavior over a wide range of temperatures

  • Easily and interactively predict and analyze atomic vibration modes

  • Understand the atomic vibrations that lead to phase transitions and chemical reactions

  • Compute thermodynamic functions from first principles in a few clicks

  • Directly simulate, compare and interpret experimental spectra:

    • Phonon dispersions from neutron scattering or EELS experiments

    • IR/Raman spectra - including LO/TO splitting

  • Applicable to solids, surfaces, interfaces, and isolated, adsorbed and intercalated molecules

  • Flexible use of multiple force engines: VASP, MOPAC, or LAMMPS

  • Use together with MedeA MLP and MLPG modules to train and validate machine-learned potentials

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Example Usage Scenarios

  • Identify crystal phases and detect defects or impurities

  • Investigate polymorphism, phase stability, and mechanisms of phase transitions

  • Inelastic neutron scattering - accurately reproducing measurements and often eliminating the need for experiments

  • Surface chemistry and catalysis

  • Temperature stability of acoustic sensors and filters

  • Temperature dependent chemical reaction and diffusion rates

  • Predict thermal expansion

  • Use as starting point for computing neutron scattering laws

MedeA Phonon effectively enables our simulations to escape the zero Kelvin prison of density functional theory. Clint Geller, NNL

The vast majority [of thermal scattering laws] were developed by MedeA users using VASP, PHONON, and LAMMPS. Michael L. Zerkle, NNL

Key Properties and Outputs

  • Phonon dispersion relations

  • Animation of the atomic vibrations associated with each phonon mode

  • Total and partial phonon density of states

  • Zero-point energy

  • Vibrational part of heat capacity, enthalpy, entropy, and free energy as a function of temperature

  • Electronic contribution to the free energy from Fermi-Dirac occupation

  • Classification and symmetry analysis of vibrational modes at the zone center

  • Infrared and Raman spectra including intensities and separation of TO and LO components

Computational Characteristics

  • Automatic detection and use of the space-group symmetry of the phase to reduce computational load

  • Fully automatic construction of supercells and the necessary atomic displacements required for the calculations

  • Fully automated setup, execution, and processing of VASP jobs

  • Uses forces computed with VASP, MOPAC, or LAMMPS. The use of Phonon with VASP includes the ability to utilize all available density functionals as well as spin polarization and fully relativistic calculations

  • Specification of constraints on atom positions. For instance, selectively obtain vibrational modes of molecules on surfaces at reduced computational cost

  • Applicable to transition state geometries, so that you can obtain vibrational partition functions for the calculation of temperature dependent reaction and diffusion rates within Eyring’s transition state theory

  • Restart capabilities in case of hardware or communication failures

  • Larger systems may involve several hundred individual tasks, which are automatically managed by the MedeA JobServer

When combined with LAMMPS and well-trained machine-learned potentials, phonon calculations can be performed even more efficiently.

Methodology

MedeA Phonon is based on the PHONON program authored by Prof. Krzysztof Parlinski [2],[3]. For most applications, the only required input is an optimized structure. Phonon typically obtains forces from ab initio methods such as MedeA VASP. Semi-empirical quantum (MedeA MOPAC) and forcefield methods (MedeA LAMMPS) are also supported.

Validation and integration

MedeA Phonon has been validated across a wide range of materials systems. Through tight integration with the powerful and user-friendly MedeA Environment, the module automates the entire phonon calculation at the click of a button. Integrated modeling, visualization, and analysis tools allow rapid interpretation of results, while detailed tutorials help new users become productive quickly.

Required Modules

  • MedeA Environment

  • MedeA Phonon

  • MedeA VASP

Supported Modules

  • MedeA LAMMPS (Part of the standard MedeA Environment)

  • MedeA MOPAC

  • MedeA Machine-Learned Potential

Find Out More

Learn how to use MedeA Phonon in the following Materials Design Application Notes:

  • Temperature-Dependent Phase Transitions of ZrO2

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