Efficient absolute interface energy calculations for heterostructures: Synergy between localized basis sets and surface passivation techniques

Heterostructures combining diverse physico-chemical properties are increasingly in demand for a wide range of applications in modern science and technology. However, despite their importance in materials science, accurately determining absolute interface energies remains a major challenge. Here, we present a computationally efficient framework for determining interface energies by incorporating a surface passivation technique, demonstrated using pseudo H passivation with a localized basis set method and an explicit chemical potential. This framework is applied to calculate absolute interface energies and analyze the electronic properties of quasi lattice matched and lattice mismatched III and V on Si interfaces, with results compared to conventional reconstructed surface calculations. By combining localized basis sets with surface passivation techniques, this framework allows for accurate estimation of absolute interface energies in heterogeneous material systems. This approach effectively addresses issues associated with surface reconstructions while significantly reducing computational costs within the framework of density functional theory, and moreover offers considerable potential for calculating interface energies across diverse material systems.

💡 Research Summary

This paper presents a novel and computationally efficient framework for calculating the absolute interface energy of heterostructures, a fundamental property critical for understanding their thermodynamic stability, bonding, and electronic behavior. The method addresses the significant challenges inherent in traditional density functional theory (DFT) approaches by synergistically combining localized basis sets with a surface passivation technique.

The primary obstacle in calculating absolute interface energy lies in isolating the interface contribution from the total energy of a slab model, which includes bulk and surface terms. Conventional methods often explicitly model the top and bottom surfaces of the slab using their known atomic reconstructions. However, this “reconstructed surface” approach is computationally demanding, sensitive to the specific reconstruction model, and requires impractically large vacuum spaces to eliminate spurious electrostatic interactions between periodic images—a requirement that is prohibitively expensive for plane-wave basis set codes.

The authors’ innovative solution, termed the CLAPS (Combined Localized basis sets and Passivated Surfaces) framework, bypasses these issues. It employs two key components: First, a surface passivation technique using pseudo-hydrogen (H*) atoms. These atoms, with charges tuned according to the host atom’s valence (e.g., 1.25e for Group III, 0.75e for Group V), saturate the dangling bonds at the slab surfaces. This effectively mimics a bulk-like electronic environment, eliminating the need for complex and computationally heavy surface reconstruction models and inherently canceling surface dipole effects. Second, the use of a localized basis set code, specifically SIESTA with numerical atomic orbitals (NAOs). Localized basis sets scale more efficiently with system size and can handle the large vacuum regions (e.g., ~400 Å in this study) necessary to fully decouple periodic slab images at a feasible computational cost, a task where plane-wave codes struggle.

The efficacy of the CLAPS method is demonstrated through applications to both quasi-lattice-matched (GaP/Si) and lattice-mismatched (GaAs/Si) III-V/Si(001) interfaces. For the GaP/Si case, the absolute interface energies calculated using the H* passivation method show excellent agreement with those obtained from established, computationally intensive calculations using reconstructed surfaces, validating the accuracy of the new approach. Furthermore, the framework incorporates an explicit chemical potential, enabling a comprehensive thermodynamic analysis of interface stability across different growth conditions.

In summary, this work introduces a robust, accurate, and highly efficient methodology for determining absolute interface energies. By overcoming the limitations of surface reconstruction modeling and the high cost of large vacuum regions in plane-wave DFT, the CLAPS framework offers a versatile tool applicable to a wide range of heterostructure systems. It promises to significantly accelerate materials discovery and optimization by providing reliable insights into interface thermodynamics and properties with greatly reduced computational resources.