OpenQP

Official Resources

• Homepage: https://github.com/Open-Quantum-Platform/openqp
• Documentation: In repository / Source code
• Source Repository: https://github.com/Open-Quantum-Platform/openqp
• License: Apache License 2.0

Overview

OpenQP (Open Quantum Platform) is a modern quantum chemistry software package developed by the Choi Group (Kyungpook National University). It features the implementation of Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory (MRSF-TDDFT). This method addresses the critical issue of spin contamination in conventional Spin-Flip TDDFT, allowing for accurate description of ground and excited states with multireference character, conical intersections, and diradicals.

Scientific domain: Multireference electronic structure, excited states, spin-flip methods, conical intersections Target user community: Electronic structure theorists, photochemists studying diradicals and bond breaking

Theoretical Methods

• Mixed-Reference Spin-Flip TDDFT (MRSF-TDDFT)
• Spin-Flip TDDFT (SF-TDDFT)
• Conventional TDDFT
• Hartree-Fock (HF) and DFT ground states
• Analytic gradients for MRSF-TDDFT
• Non-adiabatic coupling vectors (MRSF-TDDFT)
• Linear Response Theory

Capabilities (CRITICAL)

• Ground and excited state energies
• Geometry optimization (ground and excited)
• Conical intersection search (MECP)
• Non-adiabatic coupling calculation
• Correction of spin contamination
• Proper description of S0-S1 degeneracy in diradicals
• Accurate singlet-triplet gaps

Sources: GitHub repository, published papers (JCTC, JCP)

Key Strengths

MRSF-TDDFT Method:

• Eliminates spin contamination of SF-TDDFT
• Balanced description of response states
• Accurate for bond-breaking
• Accurate for conical intersections

Analytic Gradients:

• Geometry optimization for excited states
• Dynamics simulations (via PyOQP)
• MECP optimization capability

Modern Architecture:

• Python/C++ hybrid (PyOQP)
• Modular design
• Open-source license

Inputs & Outputs

• Input formats:

  • Python scripts (PyOQP)
  • Input blocks for molecules and methods

• Output data types:

  • Energies and gradients
  • Spin expectation values <S^2>
  • Optimized geometries
  • NAC vectors

Interfaces & Ecosystem

• Language: C++ core, Python interface
• Parallelization: OpenMP
• Libraries: Eigen3, Libint2
• Ecosystem: Can be used as a library or standalone

Advanced Features

Conical Intersection Optimization:

• Analytic gradients allow efficient search
• Correct topology at CX thanks to MRSF
• Avoids artifical cusps of standard TDDFT

Diradical Physics:

• Accurate singlet-triplet splitting
• Proper handling of open-shell singlets
• Double excitation retrieval

Performance Characteristics

• Speed: Comparable to standard TDDFT/SF-TDDFT
• Accuracy: Superior to TDDFT for multireference cases
• Scaling: N^3 to N^4 depending on implementation
• Parallelization: Shared memory (OpenMP)

Computational Cost

• Memory: Moderate (density matrices)
• Time: Similar to regular TDDFT linear response
• Optimization: Efficient analytic gradients

Limitations & Known Constraints

• Feature set: Focused on (SF-)TDDFT, less comprehensive than Gaussian/Q-Chem
• Basis sets: Depends on libint support
• Solvation: Functionality may be limited compared to major codes

Comparison with Other Codes

• vs Q-Chem: Q-Chem has SF-TDDFT, but MRSF-TDDFT is OpenQP's specialty
• vs PySCF: OpenQP focused on specific MRSF methodology
• vs GAMESS: OpenQP more modern C++ architecture
• Unique strength: Reference implementation of MRSF-TDDFT

Application Areas

• Photoswitches: Azobenzene, diarylethenes (conical intersections)
• Diradicals: Perylene diimide, organic magnetic materials
• Bond breaking: Photodissociation curves
• Singlet Fission: Electronic state characterization

Best Practices

• Reference State: Choose appropriate high-spin triplet reference
• Functional: BHHLYP often used for SF-TDDFT
• Validation: Check <S^2> values for spin purity
• Active Space: Implicit in SF method, check orbital ordering

Community and Support

• Open-source Apache 2.0
• Developed by Choi Group
• GitHub issues
• Academic publications serve as documentation foundation

Verification & Sources

Primary sources:

1. GitHub: https://github.com/Open-Quantum-Platform/openqp
2. Y. I. Carreras, H. Park, A. Jiang, C. H. Choi, J. Chem. Phys. 153, 214107 (2020)

Confidence: VERIFIED - Research group code

Verification status: ✅ VERIFIED

• Official homepage: ACCESSIBLE
• Source code: OPEN (Apache 2.0)
• Method: MRSF-TDDFT (Scientifically verified)
• Specialized strength: Eliminating spin contamination in SF-TDDFT