A variational 2-RDM-driven CASSCF plugin to Psi4
This plugin to Psi4 performs variational two-electron reduced-density-matrix (2-RDM)-driven complete active space self consistent field (CASSCF) computations. In principle, because variational 2-RDM (v2RDM) methods scale only polynomially with system size, vRDM-driven CASSCF computations can be performed using active spaces that are larger than can be used within conventional configuration-interaction-driven CASSCF methods. For more information regarding the performance of the method, see Refs. 2-4.
To run the Psi4 plugin v2rdm_casscf:
Download Psi4 (1.2rc2 or later) from github.com: https://github.com/psi4/psi4, and follow the installation instructions given here: http://psicode.org/psi4manual/master/build_planning.html . Make sure to keep the name of the plugin directory v2rdm_casscf.
Configure with CMake to generate a Makefile. Run
psi4 --plugin-compileto get a CMake command. Modify it as needed with
-Dfor compiler, libraries, and options.
Note that, if you configured Psi4 with a fortran compiler, you shouldn't have to specify these things here. If the configure shows no errors, compile the plugin:
If the plugin compiles without any errors, you can run a few tests:
The test directories (tests/v2rdm1, etc.) contain input files that can help you get started using v2rdm-casscf.
Or run tests through pytest
pytest -rws -v tests/
python -c "import v2rdm_casscf; v2rdm_casscf.test('quick')"
The positivity conditions enforced in the computation. Allowed values include DQG, DQ, DG, D, DQGT1, DQGT2, and DQGT1T2. The default value is DQG.
Enforce the additional condition that D3 be possitive and correctly contract to D2? Default false.
Do constrain the expectation value of spin squared? Default true.
The convergence in the primal/dual energy gap. Default 1e-4.
The convergence in the primal and dual errors. Default 1e-4.
The maximum number of outer iterations. Default 10000.
Active space specification
An array containing the number of frozen doubly-occupied orbitals per irrep. These orbitals are not included in the active space, nor are they optimized during the v2RDM-CASSCF procedure. This option trumps Psi4's NUM_FROZEN_DOCC and FREEZE_CORE options.
An array containing the number of frozen unoccupied orbitals per irrep. These orbitals are not included in the active space, nor are they optimized during the v2RDM-CASSCF procedure. This option trumps Psi4's NUM_FROZEN_UOCC option.
An array giving the number of restricted doubly-occupied orbitals per irrep. These orbitals are not included in the active space, but they are optimized by the v2RDM-CASSCF procedure.
An array giving the number of restricted unoccupied orbitals per irrep. These orbitals are not included in the active space, but they are optimized by the v2RDM-CASSCF procedure.
An array giving the number of active orbitals (occupied plus unoccupied) per irrep. This option provides a more intuitive way of specifying the active space than the FROZEN_DOCC/RESTRICTED_DOCC/RESTRICTED_UOCC/FROZEN_UOCC keywords. The simplest specification of the active space would involve this keyword and at the RESTRICTED_DOCC keyword. This option trumps the RESTRICTED_UOCC option, which will be determined from the ACTIVE, RESTRICTED_DOCC, FROZEN_DOCC, and FROZEN_UOCC arrays.
Do save progress in a checkpoint file? Default false.
Frequency of checkpoint file generation. The checkpoint file is updated every CHECKPOINT_FREQUENCY iterations. The default frequency will be ORBOPT_FREQUENCY.
File containing previous primal/dual solutions and integrals.
Integrals and SCF type
Auxiliary basis set for SCF density fitting computations. Defaults to a JKFIT basis.
What algorithm to use for the initial SCF computation. Default DF.
Tolerance for Cholesky decomposition of the ERI tensor. Default 1e-4.
Flag to optimize orbitals using a quasi one-step type approach. Default 1.
Convergence in the orbital gradient norm. Default 1e-4.
Convergence in the energy for orbital rotations. Default 1e-8.
Flag for using exact expresions for diagonal Hessian elements. Default 0.
Frequency of orbital optimization. Optimization occurs every ORBOPT_FREQUENCY iterations. Default 200.
Do rotate active/active orbital pairs? Default false.
Do write a MOLDEN output file containing the natural orbitals? If yes, the filename will end in .molden, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule. Default false.
Base filename for text files written by PSI, such as the MOLDEN output file, the Hessian file, the internal coordinate file, etc. Use the add_str_i function to make this string case sensitive.
Do write a ORBOPT output file? If so, the filename will end in .orbopt, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.
- For large jobs, when running with multiple threads, sometimes a thread will hang and the job will stall.
- For large jobs, add "ulimit -s unlimited" to .bashrc to avoid segfault when calling the fortran orbital optimization routines.
 J. M. Turney, A. C. Simmonett, R. M. Parrish, E. G. Hohenstein, F. A. Evangelista, J. T. Fermann, B. J. Mintz, L. A. Burns, J. J. Wilke, M. L. Abrams, N. J. Russ, M. L. Leininger, C. L. Janssen, E. T. Seidl, W. D. Allen, H. F. Schaefer, R. A. King, E. F. Valeev, C. D. Sherrill, and T. D. Crawford, WIREs: Comp. Molec. Sci. 2, 556 (2012). "Psi4: an open-source ab initio electronic structure program"
 J. Fosso-Tande, D. R. Nascimento, and A. E. DePrince III, Mol. Phys. 114, 423-430 (2015). "Accuracy of two-particle N-representability conditions for describing different spin states and the singlet-triplet gap in the linear acene series." http://dx.doi.org/10.1080/00268976.2015.1078008
 J. Fosso-Tande, T.-S. Nguyen, G. Gidofalvi, and A. E. DePrince III, J. Chem. Theory Comput., 12, 2260-2271 (2016). "Large-scale variational two-electron reduced-density-matrix-driven complete active space self-consistent field methods." http://dx.doi.org/10.1021/acs.jctc.6b00190
 E. Maradzike, G. Gidofalvi, J. M. Turney, H. F. Schaefer III, and A. E. DePrince III, J. Chem. Theory Comput., 13, 4113-4122 (2017). "Analytic Energy Gradients for Variational Two-Electron Reduced-Density-Matrix-Driven Complete Active Space Self-Consistent Field Theory." http://dx.doi.org/10.1021/acs.jctc.7b00366