NBSE

Official Resources

• Homepage: OCEAN Website (Distributed as part of OCEAN)
• Documentation: Referenced in OCEAN documentation
• License: Ask OCEAN developers

Overview

NBSE (NIST Bethe-Salpeter Equation solver) is the core solver engine used within the OCEAN (Obtaining Core Excitations using ABINIT and NBSE) package. Originally developed by Eric Shirley at NIST, it is designed for the accurate calculation of core-level spectroscopic properties (XAS, XES, NRIXS) using the Bethe-Salpeter Equation. It is typically not used as a standalone user-facing tool but is the computational heart of the OCEAN workflow.

Scientific Domain

• Core-Level Spectroscopy: XAS, XES
• Bethe-Salpeter Equation: Core-hole implementation
• X-ray Physics: Synchrotron theoretical support

Relationship with OCEAN

• OCEAN: The user-facing package that interfaces DFT (ABINIT/QE) with NBSE.
• NBSE: The numeric solver that handles the BSE matrix construction and diagonalization for core excitations.

Recommendation

Use OCEAN: For researchers wanting to use NBSE, the correct approach is to install and use the OCEAN package (#100), which wraps NBSE with necessary pre/post-processing and DFT interfaces.

Verification

• Status: ✅ VERIFIED (as component)
• Identity: Confirmed as "Obtaining Core Excitations using ABINIT and NBSE".
• Primary Use: Backend for OCEAN.