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, MP2 correlation, and TDHF/TDDFT with MRSF-TDDFT to treat multiconfigurational ground and excited states — diradicals, bond breaking, conical intersections, nonadiabatic dynamics, and spin-orbit coupling — through autonomous, interoperable modules. Learn it through the OpenQP manual (reference documentation for every method, workflow, and keyword; source: openqp-docs) and the hands-on OpenQP tutorials (guided, runnable end-to-end walkthroughs).
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 |
| MP2 | RHF, UHF, and ROHF references; MP2, SCS-MP2, SOS-MP2, OS/SS-MP2, SCS-MI-MP2, and custom spin scaling | Energy-only post-SCF correlation with spin-component-scaled variants |
| 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) |
Tutorials: Hartree–Fock & DFT · MP2 & spin-scaled MP2 · TDDFT/TDHF · Spin-flip TDDFT · MRSF-TDDFT · UMRSF-TDDFT
| 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 | — |
Tutorials: Hessians, frequencies & IR/Raman · NMR shielding · Spin–orbit coupling · Population, moments & charges · PCM/ddX solvation
| Workflow | runtype |
Default execution |
|---|---|---|
| Energy / gradient / Hessian | energy, grad, hess |
native |
| Minimization & transition states | optimize, ts |
native OQP |
| Conical intersections | meci, mecp, tci |
native OQP |
| Reaction paths | irc, mep, neb |
native OQP |
| Nonadiabatic data | nac, nacme |
native |
The built-in optimizer uses redundant-internal / DLC / TRIC coordinates with
restricted-step RFO/P-RFO and needs no external optimizer package. It covers
all primary geometry and reaction-path workflows above, including aligned,
endpoint-optimized climbing-image NEB and optional numerical/analytical initial
Hessians for transition-state searches. Traditional sectioned .inp files
may still select SciPy or geomeTRIC;
geomeTRIC remains an optional compatibility backend for advanced constrained
optimization.
Tutorials: Geometry optimization & TS · Conical intersections
Nonadiabatic molecular dynamics (runtype=namd) with Tully fewest-switches
surface hopping on MRSF-TDDFT states, spin-orbit-coupled intersystem crossing,
and ESPF QM/MM embedding. These compose into SOC-NAMD-QMMM: excited-state
surface-hopping dynamics of an MRSF-TDDFT chromophore, with singlet/triplet
intersystem crossing, embedded in an explicit (OpenMM) MM solvent.
- Native fewest-switches surface hopping (
runtype=namd) for gas-phase MRSF-TDDFT internal conversion. - SOC-NAMD for intersystem crossing: SHARC-like spin-adiabatic propagation and an MCH-basis mode with exact active-root MCH gradients (
[md] soc_basis=mch). - ESPF electrostatic QM/MM via OpenMM (PME periodic electrostatics, smooth ESPF grid forces, rigid-water constraints); QM/MM composes with both FSSH and SOC-NAMD to give SOC-NAMD-QMMM.
- Overlap-based MRSF state tracking, finite-difference NAC/TDC propagation, and energy-based decoherence (EDC).
Tutorials: SOC-NAMD-QMMM · ESPF QM/MM embedding
See the SOC-NAMD-QMMM guide and the [md] / [qmmm] keyword pages in the
manual
for complete input decks and the compact job.qmmm(...) / job.workflow.namd(...)
Python API.
| 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 |
Tutorials: SCF convergence & guesses · Effective core potentials
| 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 |
- Full analytic spin-adiabatic SOC gradients, requiring MCH derivative-coupling vectors and SOC-gradient matrix elements.
- Scalar-relativistic (X2C) framework extending the relativistic MRSF-TDDFT treatment
pip install openqpThe native optimizer is included by default. Install the optional legacy geomeTRIC backend only when it is needed:
pip install 'openqp[geometric]'For 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 # default mixed regression suiteEvery legacy example has a concise .oqp companion. Select which input syntax
the regression runner uses with --input-format:
openqp --run_tests all --input-format inp # standard suite through .inp
openqp --run_tests all --input-format oqp # standard suite through .oqp
openqp --run_tests all --input-format both # both syntaxes in that suiteOmitting the selector uses auto: it prefers .oqp, retains any legacy-only
.inp, and keeps a small representative .inp compatibility set. The
historical all scope still excludes unusually slow or non-self-contained
examples; selecting an explicit directory applies the requested format to every
input in that directory. Each calculation receives an isolated output folder,
so paired optimization artifacts cannot overwrite one another.
Control OpenMP threads per process or MPI rank with --omp 16 or [input] omp_threads=16.
- OpenQP Manual (reference docs; source: openqp-docs)
- OpenQP Tutorials (guided, runnable walkthroughs)
- Build options
- API guide
- Example inputs
- 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.