Official Resources
- Homepage: https://opium.sourceforge.net/index.html
- Source Repository: https://github.com/rappegroup/opium
- Documentation: https://opium.sourceforge.net/guide.html
- License: Open-source (free for academic and non-commercial use)
Overview
OPIUM (Open-source Pseudopotential Interface / Unification Module) is a program for generating norm-conserving pseudopotentials for ab initio electronic structure calculations. Developed by the Rappe group at the University of Pennsylvania, it provides a comprehensive toolset for constructing, testing, and exporting pseudopotentials in formats compatible with major DFT codes. OPIUM supports scalar-relativistic, fully-relativistic, and non-relativistic pseudopotential generation.
The code implements multiple pseudopotential construction methods including Optimized (RRKJ), Kerker, and Troullier-Martins schemes. It includes support for partial core correction, ghost state checking, and transferability testing across multiple atomic configurations. OPIUM can output pseudopotentials in formats for Quantum ESPRESSO, CASTEP, ABINIT, PWSCF, and other popular DFT packages.
Scientific domain: Electronic structure theory, pseudopotential generation
Target user community: Computational chemists and physicists developing pseudopotentials for DFT calculations
Theoretical Methods
- Scalar-relativistic, fully-relativistic, and non-relativistic pseudopotential generation
- Optimized (RRKJ) pseudopotential construction
- Kerker pseudopotential construction
- Troullier-Martins pseudopotential construction
- Partial core correction (Louie-Froyen-Cohen and Fuchs-Scheffler)
- Ghost state checking (Gonze-Stumpf-Scheffler method)
- Designed non-local potential approach (Ramer-Rappe)
- Support for LDA, GGA, Hartree-Fock, hybrid, and range-separated hybrid XC functionals
Capabilities (CRITICAL)
- All-electron atomic solve and pseudopotential construction
- Transferability testing across multiple configurations
- Ghost state detection and checking
- Automatic plotting of wavefunctions, potentials, and density
- Multiple output formats: .upf (QE), .recpot (CASTEP), .fhi (ABINIT/JDFTx), .ncpp (PWSCF), .pwf, .cpi
- Semicore state support
- Kinetic energy optimization (RRKJ method)
- XC functional support via Libxc
Inputs & Outputs
Input formats:
- OPIUM parameter files with flexible keyblock format
- Atomic configuration specifications
- XC functional and pseudopotential type selection
Output data types:
- Pseudopotential files in multiple formats (.upf, .recpot, .fhi, .ncpp, .pwf, .cpi)
- All-electron and pseudo wavefunctions
- Transferability test results
- Ghost state analysis reports
- Plot files (via xmgrace)
Interfaces & Ecosystem
- Programming language: C and Fortran
- Output compatibility: Quantum ESPRESSO, CASTEP, ABINIT, JDFTx, PWSCF, FHI98md
- XC functionals: Via Libxc library
- Plotting: xmgrace integration
Limitations & Known Constraints
- Requires C and Fortran compilers to build from source
- Does not work with g77 compiler
- Parameter file format requires learning the keyblock syntax
- Pre-compiled binaries available only for Linux/x86 and MacOSX
- Not all XC functionals available in older versions
Performance Characteristics
- Single-atom calculations, very fast (seconds to minutes)
- Transferability testing involves multiple atomic configurations
- No parallelization needed for typical use
- Memory requirements minimal
Comparison with Other Codes
- vs APE: Both generate norm-conserving pseudopotentials; OPIUM offers more construction methods (RRKJ, Kerker, TM) and ghost state checking
- vs ATOMPAW: ATOMPAW generates PAW potentials; OPIUM focuses on norm-conserving pseudopotentials
- vs PSEUDODOJO: PSEUDODOJO is a library of pre-generated potentials; OPIUM is a generation tool
Best Practices
- Always run transferability tests for target chemical environments
- Check for ghost states after generation
- Use partial core correction for systems with significant core-valence overlap
- Test pseudopotentials against all-electron results for reference systems
- Use the designed non-local approach for improved transferability
Verification & Sources
Primary sources:
- Official website: https://opium.sourceforge.net/index.html
- GitHub repository: https://github.com/rappegroup/opium
- Documentation: https://opium.sourceforge.net/guide.html
Confidence: VERIFIED - SourceForge and GitHub repositories confirmed accessible