A variational 2-RDM-driven CASSCF plugin to Psi4
##OVERVIEW
This plugin to Psi4[1] performs variational two-electron reduced-density-matrix (2-RDM)-driven complete active space self consistent field (CASSCF) computations. In principle, because variational 2-RDM (v-2RDM) methods scale only polynomially with system size, v-2RDM-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. 2-3.
##INSTALLATION
To run the psi4 plugin v2rdm_casscf:
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Download psi4public from github.com: https://github.com/psi4/psi4public, and follow the installation instructions given here: http://www.psicode.org/.
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Modify the setup script by specifying your fortran compiler, options, and libraries
cd v2rdm_casscf
vi setup
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Modify F90, F90_FLAGS, and F90_LIB, as needed.
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Compile the plugin:
./setup
##INPUT OPTIONS
###N-representability conditions
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POSITIVITY (string):
The positivity conditions enforced in the computation. Allowed values include DQG, DQ, DG, D, DQGT1, DQGT2, and DQGT1T2. The default value is DQG.
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CONSTRAIN_D3 (bool):
Enforce the additional condition that D3 be possitive and correctly contract to D2? Default false.
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CONSTRAIN_SPIN (bool):
Do constrain the expectation value of spin squared? Default true.
###Convergence
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E_CONVERGENCE (double):
The convergence in the primal/dual energy gap. Default 1e-4.
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R_CONVERGENCE (double):
The convergence in the primal and dual errors. Default 1e-4.
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MAXITER (int):
The maximum number of outer iterations. Default 10000.
###Active space specification
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FROZEN_DOCC (array):
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.
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FROZEN_UOCC (array):
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.
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RESTRICTED_DOCC (array):
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.
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RESTRICTED_UOCC (array):
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.
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ACTIVE (array):
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.
###Restarting jobs
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WRITE_CHECKPOINT_FILE (bool):
Do save progress in a checkpoint file? Default false.
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CHECKPOINT_FREQUENCY (bool):
Frequency of checkpoint file generation. The checkpoint file is updated every CHECKPOINT_FREQUENCY iterations. The default frequency will be ORBOPT_FREQUENCY.
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RESTART_FROM_CHECKPOINT_FILE (string):
File containing previous primal/dual solutions and integrals.
###Integrals and SCF type
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DF_BASIS_SCF (string):
Auxiliary basis set for SCF density fitting computations. Defaults to a JKFIT basis.
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SCF_TYPE (string):
What algorithm to use for the initial SCF computation. Default DF.
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CHOLESKY_TOLERANCE (double):
Tolerance for Cholesky decomposition of the ERI tensor. Default 1e-4.
###Orbital optimization
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ORBOPT_ONE_STEP (int):
Flag to optimize orbitals using a quasi one-step type approach. Default 1.
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ORBOPT_GRADIENT_CONVERGENCE (double):
Convergence in the orbital gradient norm. Default 1e-4.
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ORBOPT_ENERGY_CONVERGENCE (double):
Convergence in the energy for orbital rotations. Default 1e-8.
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ORBOPT_EXACT_DIAGONAL_HESSIAN (int):
Flag for using exact expresions for diagonal Hessian elements. Default 0.
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ORBOPT_FREQUENCY (int):
Frequency of orbital optimization. Optimization occurs every ORBOPT_FREQUENCY iterations. Default 200.
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ORBOPT_ACTIVE_ACTIVE_ROTATIONS (bool):
Do rotate active/active orbital pairs? Default false.
###Additional files
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MOLDEN_WRITE (bool):
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.
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WRITER_FILE_LABEL (string):
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.
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ORBOPT_WRITE (bool):
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.
##KNOWN ISSUES
- 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.
##REFERENCES
[1] 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"
[2] 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
[3] J. Fosso-Tande, T.-S. Nguyen, G. Gidofalvi, and A. E. DePrince III, J. Chem. Theory Comput., accepted (2016). "Large-scale v2RDM-driven CASSCF methods." http://dx.doi.org/10.1021/acs.jctc.6b00190