30 December 2024
Density functional Bogoliubov-de Gennes theory for superconductors implemented in the SIESTA code
A novel approach has been designed for the computational study of superconducting materials through the development of SIESTA-BdG, a method that combines the Bogoliubov-de Gennes (BdG) formalism with Density Functional Theory (DFT) inside the SIESTA code. This novel computational tool enables accurate, first-principles simulations of both conventional and unconventional superconducting systems, including complex materials and device architectures.
Superconductivity remains one of the most fascinating quantum phenomena, with implications from energy transmission to quantum computing. However, modeling superconductors, especially unconventional ones, poses significant theoretical and computational challenges. The SIESTA-BdG method addresses these challenges by implementing a semi-phenomenological version of superconducting DFT (SCDFT) within a localized basis framework.
The strength of SIESTA-BdG lies in its ability to simulate superconducting properties (e.g., charge densities, band structures, and superconducting gaps) with high efficiency and accuracy. The novel approach enables the study of both bulk materials and inhomogeneous systems, including heterostructures and interfaces that are key to designing next-generation superconducting devices. Importantly, it supports spin-orbit coupling, allowing simulations that explore the interplay of topology and superconductivity, which is critical for topological quantum computing.
The authors of the study have demonstrated the power of such a computational tool by applying it to a range of test cases: the conventional superconductors niobium (Nb) and lead (Pb), and the unconventional superconductor iron selenide (FeSe). The simulations accurately reproduced experimental observations and matched results from other advanced codes, such as KKR-BdG. Furthermore, the framework was extended to model quantum transport through superconducting devices using nonequilibrium Green's function (NEGF) techniques. As a proof of concept, the team studied Andreev reflection in a carbon nanotube-superconductor junction, showing the method's versatility in realistic device simulations.
SIESTA-BdG opens new pathways for simulating superconductivity in both fundamental and applied settings. Its integration into the SIESTA code ensures scalability, accuracy, and user accessibility. This advancement strengthens the role of first-principles methods in exploring superconducting mechanisms, designing devices, and understanding quantum materials.
About the SIESTA Code
SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) is a leading open-source DFT code that uses pseudopotentials and a localized basis set. It is known for its computational efficiency and scalability, making it suitable for large systems and high-throughput simulations. SIESTA includes robust implementations of structural, electronic, magnetic, and transport properties. Its integration with linear-scaling solvers and support for spin-orbit coupling further extend its capabilities. With a large user community and extensive documentation, SIESTA is a reliable platform for materials simulations, now enhanced with superconductivity modeling through the SIESTA-BdG extension.
Reference article
Reho, N. Wittemeier, A.H. Kole, O. Ordejon, and Z. Zanolli, Physical Review B 110, 13, 134505