Open Quantum Platform (OpenQP) is a quantum chemical platform built around Mixed-Reference Spin-Flip (MRSF)-TDDFT with an emphasis on an open-source ecosystem. It combines conventional HF/DFT and TDHF/TDDFT with MRSF-TDDFT to treat multiconfigurational ground and excited states — diradicals, bond breaking, conical intersections, nonadiabatic dynamics, and spin-orbit coupling — using autonomous, interoperable modules driven through the PyOQP Python wrapper.
MRSF-TDDFT is the central scientific feature of OpenQP: it retains the practical linear-response structure of TDDFT while removing the spin contamination that limits conventional spin-flip TDDFT, making it useful for multiconfigurational ground-state surfaces as well as excited-state and photochemical workflows.
| Method | References / variants | Notes |
|---|---|---|
| Hartree–Fock | RHF, ROHF, UHF | Closed- and open-shell SCF foundations |
| DFT | RKS / UKS / ROKS via LibXC | Hundreds of LCAO functionals; range-separated (CAM/LRC) support |
| TDHF / TDDFT | RPA, TDA | Conventional linear-response excited states |
| SF-TDDFT | Spin-flip TDA | Spin-flip excited states from a high-spin reference |
| MRSF-TDDFT | Mixed-Reference Spin-Flip + DTCAM-series functionals | Main production method; multireference accuracy with LR practicality |
| UMRSF-TDDFT | MRSF excitation energies from a UHF reference | Energy-only |
| MRSF-EKT | IP/EA via Extended Koopmans' Theorem | Dyson orbitals and pole strengths (runtype=ekt) |
| Capability | Scope | Notes |
|---|---|---|
| Analytic gradients | HF, DFT, TDDFT, SF/MRSF-TDDFT | State-specific gradients for optimization and dynamics |
| Hessians | Native analytic HF/DFT Hessians + numerical Hessians | Covers UHF/ROHF references, ECPs, and CAM/LRC functionals |
| Vibrational analysis | Frequencies, normal modes, thermochemistry, IR and Raman intensities | Native dipole / CPHF-polarizability kernels |
| NMR shieldings | CGO and GIAO (London-orbital) gauges | HF and DFT, closed- and open-shell |
| Nonadiabatic couplings | NAC / NACME between MRSF-TDDFT states | TLF technology for dynamics workflows |
| Spin-orbit coupling | SOC between MRSF-TDDFT states | One- and two-electron contributions (Relativistic MRSF-TDDFT) |
| X-ray absorption | XAS / core-excitation workflows (incl. ΔCHP-MRSF) | Core-level excited states |
| Implicit solvation | PCM via the ddX backend (ddCOSMO / ddPCM / ddLPB) | Energy-only continuum solvent on RHF/ROHF references |
| Population & moments | Mulliken, Löwdin, RESP charges; electric multipole moments | runtype=prop |
| Dispersion | DFT-D4 correction | — |
| Workflow | runtype |
Backends |
|---|---|---|
| Energy / gradient / Hessian | energy, grad, hess |
native |
| Minimization & transition states | optimize, ts |
oqp (native), geomeTRIC, SciPy |
| Conical intersections | meci, mecp, tci |
oqp, geomeTRIC, SciPy |
| Reaction paths | irc, mep, neb |
oqp, geomeTRIC, SciPy |
| Nonadiabatic data | nac, nacme |
native |
The built-in native optimizer (lib=oqp) uses redundant-internal / DLC / TRIC coordinates with a restricted-step RFO step and needs no external optimizer package.
| Area | What OpenQP provides |
|---|---|
| Initial guesses | Native hcore, huckel, modhuckel, minao, sap; json restart and auto; optional PySCF (sad/sap/pyscf) guesses |
| SCF convergence | DIIS family (C/E/A/V-DIIS), SOSCF, and OpenQP's own native TRAH (Trust-Region Augmented Hessian) solver, with the external OpenTrustRegion library as an optional alternative |
| Symmetry | Point-group detection; MO/state/mode labels; petite-list reductions accelerating integrals, XC, gradients, and response |
| DFT grids | Lebedev plus SG-0/SG-1/SG-2/SG-3 pruned grids with per-element DE2 radial quadrature; OpenMP-parallel XC kernels |
| Excited-state robustness | Davidson auto-restart; MINRES/AUTO Z-vector fallbacks |
| Parallelism & deployment | OpenMP and MPI; BLAS/LAPACK optimization; pip install and Docker images |
| Integration | Purpose |
|---|---|
| LibXC | Wide library of exchange-correlation functionals |
| basis_set_exchange | Standard basis sets |
| libecpint | Effective Core Potentials |
| DFT-D4 | Dispersion correction |
| PyRAI2MD | AI-driven ab initio molecular dynamics |
| Molden format | Visualization compatible with common graphics tools |
| OpenqpView | Browser-based inspection of log, JSON, Molden, cube, and XYZ outputs |
| Optional DFTB+ backend | Ground-state energy, gradient, and geometry optimization |
| Optional MOKIT | Broader external wavefunction conversion workflows |
- Efficient electrostatic embedding QM/MM by ESPF QM/MM
- Scalar-relativistic (X2C) framework extending the relativistic MRSF-TDDFT treatment
pip install openqpFor a source checkout:
git clone https://github.com/Open-Quantum-Platform/openqp.git
cd openqp
pip install .The package install keeps the Python wrapper, native library, headers, and data files together for normal openqp command-line use. A ready-to-use Docker image is also available. Build options (MPI, LibXC/ERI backends, BLAS/LAPACK selection) are documented in the Build options guide.
openqp examples/HF/H2O_RHF-HF_ENERGY.inp # OpenMP / sequential run
mpirun -np <n> openqp any_example_file.inp # MPI run
openqp --run_tests all # run the packaged example testsControl OpenMP threads per process or MPI rank with --omp 16 or [input] omp_threads=16.
- OpenQP Web — prepare inputs and preview structures locally in the browser.
- OpenQP Input Generator — browser-based input builder.
- OpenqpView — inspect OpenQP log, JSON, Molden, cube, and XYZ outputs in the browser; files are processed locally and never uploaded.
If you use OpenQP in your research, please cite the OpenQP platform paper:
- Mironov V, Komarov K, Li J, Gerasimov I, Mazaheri M, Park W, Lashkaripour A, Oh M, Nakata H, Ishimura K, Huix-Rotllant M, Lee S, and Choi CH. "OpenQP: A Quantum Chemical Platform Featuring MRSF-TDDFT with an Emphasis on Open-source Ecosystem" Journal of Chemical Theory and Computation, 2024
Original MRSF-TDDFT theory and analytic-gradient papers:
- Lee S, Filatov M, Lee S, and Choi CH. "Eliminating Spin-Contamination of Spin-Flip Time-Dependent Density Functional Theory Within Linear Response Formalism by the Use of Zeroth-Order Mixed-Reference (MR) Reduced Density Matrix." The Journal of Chemical Physics, vol. 149, no. 10, 2018.
- Lee S, Kim EE, Nakata H, Lee S, and Choi CH. "Efficient Implementations of Analytic Energy Gradient for Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory (MRSF-TDDFT)." The Journal of Chemical Physics, vol. 150, no. 18, 2019.
Recent MRSF-TDDFT accounts and overview papers:
- Park W, Komarov K, Lee S, and Choi CH. "Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory: Multireference Advantages with the Practicality of Linear Response Theory." The Journal of Physical Chemistry Letters. 2023 Sep 28;14(39):8896-908.
- Lee S, Park W, and Choi CH. "Expanding Horizons in Quantum Chemical Studies: The Versatile Power of MRSF-TDDFT." Accounts of Chemical Research, 2025.
- Park W, Lee S, Komarov K, Mironov V, Nakata H, Zeng T, Huix-Rotllant M, and Choi CH. "MRSF-TDDFT: A New Tool in Quantum Chemistry for Better Understanding Molecules and Materials." Bulletin of the Korean Chemical Society, 2025.
Principal Investigator
- Cheol Ho Choi (PI), Kyungpook National University, South Korea, cheolho.choi@gmail.com, https://www.openqp.org
Development team
- Seunghoon Lee, Seoul National University, South Korea, seunghoonlee89@gmail.com
- Vladimir Mironov, vladimir.a.mironov@gmail.com
- Konstantin Komarov, constlike@gmail.com
- Jingbai Li, Hoffmann Institute of Advanced Materials, China, lijingbai2009@gmail.com
- Igor Gerasimov, i.s.ger@yandex.ru
- Hiroya Nakata, Fukui Institute for Fundamental Chemistry, Japan, nakata.hiro07@gmail.com
- Mohsen Mazaherifar, Kyungpook National University, South Korea, moh.mazaheri@gmail.com
See the separate LICENSE file.