Ab Initio Study of Structural Instabilities and High-Pressure Equations of State in Magnesium Silicates

International Journal of Physics | Vol. 17, No. 8, August 2026 | pp. 129–136

DOI: 10.46882/2026/IJP/000205

Research Article

Title: Ab Initio Study of Structural Instabilities and High-Pressure Equations of State in Magnesium Silicates

Names of Authors: S. P. Nair¹, J. K. Greenwood²

Authors’ Affiliations:
¹ Department of Physics, University of Kerala, Trivandrum, India
² Department of Earth Sciences, University of Cambridge, Cambridge, UK

Abstract: Investigating the structural behaviour of magnesium compounds under extreme pressures is essential for developing accurate interior models of terrestrial exoplanets and gas giants. We investigated the high-pressure structural phase transitions, elastic constants, and electronic properties of MgSiO³ post-perovskite using ab initio density functional theory within the generalized gradient approximation. The computational model evaluated pressures ranging from 0.0 GPa up to 300.0 GPa. Our total-energy calculations indicate that the system undergoes a structural phase transition to a denser phase at a hydrostatic pressure of 215.0 GPa. This structural transition induces a significant volume collapse of 6.2% at the transition point. We calculated the elastic constants across the entire pressure range to verify mechanical stability. The primary phase meets all Born stability criteria until it approaches the transition pressure, where the shear modulus drops sharply. The electronic density of states revealed that the wide insulator band gap shrinks steadily from 7.80 eV at 0.0 GPa to 5.15 eV at 200.0 GPa. Upon transitioning to the high-pressure phase, the band gap decreases further to 3.90 eV at 300.0 GPa, indicating that the system remains an insulator even under ultra-high core pressures. These precise equations of state provide reliable reference parameters for deep-mantle planetary geophysics.

Keywords: Magnesium silicates; Density functional theory; Phase transition; High pressure; Elastic constants; Equation of state

Manuscript Timeline: Received: June 15, 2026 / Revised: July 18, 2026 / Accepted: August 04, 2026 / Published: August 21, 2026

Citation: Nair, S. P., & Greenwood, J. K. (2026). Ab Initio Study of Structural Instabilities and High-Pressure Equations of State in Magnesium Silicates. International Journal of Physics, 17(8), 129–136.

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