InterPhon: Ab initio interface phonon calculations within a 3D electronic structure framework*

Abstract

This work provides the community with an easily executable open-source Python package designed to automize the evaluation of Interfacial Phonons (InterPhon). Its strategy of arbitrarily defining the interfacial region and periodicity alleviates the excessive computational cost in applying ab initio phonon calculations to interfaces and enables efficient extraction of interfacial phonons. InterPhon makes it possible to apply all of the phonon-based predictions that have been available for bulk systems, to interfacial systems. The first example, in which this package was applied to InAs surfaces, demonstrates a systematic structure search for unexplored surface reconstructions, navigated by the imaginary mode of surface phonons. It eventually explains the anisotropic surface vibrations of the polar crystal. The second example, involving oxygen adsorption on Cu, reveals adsorption-induced vibrational change and its contribution to energetic stability. The third example, on a Si/GaAs interface, shows distinct vibrational patterns depending on interfacial structures. It leads to a prediction regarding the structural transition of interfaces and unveils the processing conditions for spontaneous growth of GaAs nanowires on Si. Highlevel automation in InterPhon will be of great help in elucidating interfacial atomic dynamics and in implementing an automated computational workflow for diverse interfacial systems. Program summary Program title: InterPhon CPC Library link to program files: https://doi .org /10 .17632 /9xjh66g4z2 .1 Developer's repository link: https://github .com /inwonyeu /interphon Code Ocean capsule: https://codeocean .com /capsule /4380849 Licensing provisions: LGPLv2.1 Programming language: Python Supplementary material: a PDF file describing details of phonon formalism using FDM, validation of symmetry functionality, InterPhon package architecture, method to define the interfacial region and convergence test, and calculation details for all of the results in this work. Nature of problem: The interface possesses diverse atomic structures and lattice vibrations, which are distinct from the bulk. In particular, interfacial phonons play the key roles to unveil the largely unexplored atomic dynamics within the localized region, and this information is essential to make a prediction regarding the dependence of interface structures on process conditions. However, there has been a limitation in applying ab initio phonon calculations to interfaces due to the excessive computational cost, introduced by their large number of atoms and broken symmetry. The problems are intrinsically inevitable within a three-dimensional (3D) DFT framework representing interfacial systems by supercells. Solution method: Although the main obstacles are unavoidable, distinct interfacial phonons are confined to the vicinity of the interface. By limiting the range of phonon calculations to user-defined interfacial region, the enormous computational cost is mitigated. The strategy is efficiently implemented in a Python library capable of calculation setup, evaluation, analysis, and visualization for arbitrary interfacial systems