CheMPS2/CASPT2.cpp contains an implementation of internally contracted CASPT2. The user can specify an IPEA shift and/or an imaginary level shift to mitigate possible intruder state problems. The linear CASPT2 equations can be solved with either Davidson's algorithm, or with the conjugate gradient method. Note that the overlap matrix is always diagonalized, and that a cumulant approximation of the 4-RDM should therefore be avoided.

CheMPS2/CASSCF.cpp contains the functionality to construct the active space Hamiltonian for DMRG-SCF.

CheMPS2/CASSCFdebug.cpp contains two functions: one for calculating the ROHF energy; and one for fetching FCI coefficients to determine the point group symmetry of certain electronic states of the iron dimer.

CheMPS2/CASSCFnewtonraphson.cpp contains all DMRG-SCF functions which are specific to the augmented Hessian Newton-Raphson update scheme, including the functions to calculate the gradient and Hessian.

CheMPS2/CASSCFpt2.cpp provides the interface between the CASSCF and CASPT2 classes. The routines for the 3-RDM and the Fock operator contraction with the 4-RDM are called here.

CheMPS2/ConjugateGradient.cpp is an implementation of the conjugate gradient algorithm, in the style of the Davidson class.

CheMPS2/ConvergenceScheme.cpp contains all functions of the ConvergenceScheme class, which contains the instructions for the subsequent DMRG sweeps.

CheMPS2/Correlations.cpp contains all the functionality to calculate the spin, density, and spin-flip correlation functions as well as the two-orbital mutual information.

CheMPS2/Cumulant.cpp contains static member functions to reconstruct the 4-RDM from lower order reduced density matrices. There is also a fast contraction of the Fock operator with the cumulant-reconstructed 4-RDM.

CheMPS2/Davidson.cpp is an implementation of Davidson's algorithm, both for eigenvalue problems and linear equations.

CheMPS2/DIIS.cpp contains a DIIS convergence speed-up for DMRG-SCF.

CheMPS2/DMRG.cpp contains the constructor and destructor of the DMRG class, as well as the top-level sweep functions.

CheMPS2/DMRGfock.cpp contains the functionality to express a symmetry (spin, particle number, and point group) conserving single-particle excitation on top of an MPS as a new MPS.

CheMPS2/DMRGmpsio.cpp contains the store and load functions for the DMRG checkpoint file (the MPS and the SyBookkeeper).

CheMPS2/DMRGoperators3RDM.cpp contains all update functions for the renormalized operators specific for the ThreeDM and the Correlations.

CheMPS2/DMRGoperators.cpp contains all functions related to the DMRG renormalized operators: saving to disk, loading from disk, and updating.

CheMPS2/DMRGSCFindices.cpp contains the index conversions for the DMRG-SCF algorithm.

CheMPS2/DMRGSCFintegrals.cpp is a container class for two-body matrix elements with at most two virtual indices.

CheMPS2/DMRGSCFmatrix.cpp is a container class for orbital matrices which are blockdiagonal in the irreps.

CheMPS2/DMRGSCFoptions.cpp is a container class to pass the DMRG-SCF options to the augmented Hessian Newton-Raphson and CASPT2 routines of the CASSCF class.

CheMPS2/DMRGSCFrotations.cpp contains static member functions for the two-body matrix element rotations for the CASSCF and Edmiston-Ruedenberg classes.

CheMPS2/DMRGSCFunitary.cpp contains the storage and handling of the unitary matrix and its nonredundant skew-symmetric parametrization required for the DMRG-SCF algorithm.

CheMPS2/DMRGSCFwtilde.cpp is a container class to store an intermediate for the DMRG-SCF Hessian.

CheMPS2/DMRGtechnics.cpp contains the functions related to the RDM and excited-state calculations.

CheMPS2/EdmistonRuedenberg.cpp contains an orbital localization function based on the Edmiston-Ruedenberg cost function and an augmented Hessian Newton-Raphson optimizer. It also contains the functionality to compute the Fiedler vector of the exchange matrix, to reorder the active space orbitals in a black-box fashion.

CheMPS2/Excitation.cpp contains matrix-vector multiplication routines for spin-conserving single-particle excitations.

CheMPS2/FCI.cpp contains a fast determinant-based full configuration interaction (FCI) solver. The eigenvalue problem is solved with Davidson's algorithm. Green's functions can also be computed.

CheMPS2/FourIndex.cpp contains all functions of the FourIndex container class for the two-body matrix elements.

CheMPS2/Hamiltonian.cpp contains all functions of the Hamiltonian class, including functions to get or set specific variables, as well as to save and load the Hamiltonian on disk.

CheMPS2/Heff.cpp contains top-level functions to perform the DMRG effective Hamiltonian times vector multiplication for Davidson's algorithm.

CheMPS2/HeffDiagonal.cpp contains the functions to calculate the diagonal elements of the effective Hamiltonian. These are required as preconditioner in Davidson's algorithm.

CheMPS2/HeffDiagrams1.cpp contains a subset of functions to perform the effective Hamiltonian times guess vector multiplication.

CheMPS2/HeffDiagrams2.cpp contains a subset of functions to perform the effective Hamiltonian times guess vector multiplication.

CheMPS2/HeffDiagrams3.cpp contains a subset of functions to perform the effective Hamiltonian times guess vector multiplication.

CheMPS2/HeffDiagrams4.cpp contains a subset of functions to perform the effective Hamiltonian times guess vector multiplication.

CheMPS2/HeffDiagrams5.cpp contains a subset of functions to perform the effective Hamiltonian times guess vector multiplication.

CheMPS2/Initialize.cpp sets the seed of the random number generator and cout.precision (added for PyCheMPS2).

CheMPS2/Irreps.cpp contains the psi4 symmetry conventions.

CheMPS2/Molden.cpp contains the functionality to rotate an R(O)HF molden file generated by molpro or psi4 to the new CAS space defined by the DMRGSCFunitary HDF5 checkpoint file.

CheMPS2/PrintLicense.cpp contains a function which prints the license disclaimer.

CheMPS2/Problem.cpp contains all Problem class functions. This wrapper class allows to set the desired symmetry sector for the DMRG algorithm. It allows to compute fourfold permutation symmetric Hamiltonians with DMRG (see tests 9 and 12).

CheMPS2/Sobject.cpp contains all Sobject class functions. This class constructs, stores, and decomposes the reduced two-site object.

CheMPS2/SyBookkeeper.cpp contains all SyBookkeeper functions. This class keeps track of the FCI and DMRG virtual dimensions of all symmetry sectors at all boundaries.

CheMPS2/Tensor3RDM.cpp contains all initialization functions for the spin-reduced renormalized operators of three second quantized operators.

CheMPS2/TensorF0.cpp contains all TensorF0 functions. This class stores and handles the reduced spin-0 part of two sandwiched second quantized operators, of which the particle symmetry sectors are equal.

CheMPS2/TensorF1.cpp contains all TensorF1 functions. This class stores and handles the reduced spin-1 part of two sandwiched second quantized operators, of which the particle symmetry sectors are equal.

CheMPS2/TensorGYZ.cpp contains the contruct and update functions for the G-, Y-, and Z-tensors. They are required for the two-orbital mutual information.

CheMPS2/TensorKM.cpp contains the contruct and update functions for the K- and M-tensors. It is required for the two-orbital mutual information.

CheMPS2/TensorL.cpp contains all TensorL functions. This class stores and handles the reduced spin-1/2 part of a single sandwiched second quantized operator. The class has been updated to allow for a different bra and ket wavefunction, which is needed for CheMPS2/DMRGfock.cpp.

CheMPS2/TensorO.cpp handles the tensors required to calculate the overlap between two MPSs.

CheMPS2/TensorOperator.cpp implements the storage and handling of tensor operators with a given spin, particle number, and point group irrep. It replaces the deprecated TensorDiag, TensorSwap, TensorS0Abase, TensorS1Bbase, TensorF0Cbase, TensorF1Dbase, TensorA, TensorB, TensorC, and TensorD classes.

CheMPS2/TensorQ.cpp contains all TensorQ functions. This class stores and handles the complementary reduced spin-1/2 part of three sandwiched second quantized operators.

CheMPS2/TensorS0.cpp contains all TensorS0 functions. This class stores and handles the reduced spin-0 part of two sandwiched second quantized operators, of which the particle symmetry sectors differ by 2.

CheMPS2/TensorS1.cpp contains all TensorS1 functions. This class stores and handles the reduced spin-1 part of two sandwiched second quantized operators, of which the particle symmetry sectors differ by 2.

CheMPS2/TensorT.cpp contains all TensorT functions. This class stores and handles the reduced part of an MPS site-tensor. It also contains the functionality for QR- and LQ-decomposition of MPS tensors.

CheMPS2/TensorX.cpp contains all TensorX functions. This class stores and handles the complementary reduced spin-0 part of four sandwiched second quantized operators, which is of course diagonal in the symmetry sectors.

CheMPS2/ThreeDM.cpp contains all functions to calculate and store the 3-RDM from the DMRG-optimized MPS.

CheMPS2/TwoDM.cpp contains all functions to calculate and store the 2-RDM from the DMRG-optimized MPS.

CheMPS2/TwoIndex.cpp contains all functions of the TwoIndex container class for the one-body matrix elements.

CheMPS2/Wigner.cpp contains static member functions to compute Wigner 3j, 6j, and 9j symbols. The API has been chosen to match GSL's gsl_sf_coupling_3j, gsl_sf_coupling_6j, and gsl_sf_coupling_9j.

CheMPS2/executable.cpp builds to the chemps2 executable, which allows to use libchemps2 from the command line.

CheMPS2/include/chemps2/CASPT2.h contains the definitions of the CASPT2 class.

CheMPS2/include/chemps2/CASSCF.h contains the definitions of the CASSCF class.

CheMPS2/include/chemps2/ConjugateGradient.h contains the definitions of the ConjugateGradient class.

CheMPS2/include/chemps2/ConvergenceScheme.h contains the definitions of the ConvergenceScheme class.

CheMPS2/include/chemps2/Correlations.h contains the definitions of the Correlations class.

CheMPS2/include/chemps2/Cumulant.h contains the definitions of the Cumulant class.

CheMPS2/include/chemps2/Davidson.h contains the definitions of the Davidson class.

CheMPS2/include/chemps2/DIIS.h contains the definitions of the DIIS class.

CheMPS2/include/chemps2/DMRG.h contains the definitions of the DMRG class.

CheMPS2/include/chemps2/DMRGSCFindices.h contains the definitions of the DMRGSCFindices class.

CheMPS2/include/chemps2/DMRGSCFintegrals.h contains the definitions of the DMRGSCFintegrals class.

CheMPS2/include/chemps2/DMRGSCFmatrix.h contains the definitions of the DMRGSCFmatrix class.

CheMPS2/include/chemps2/DMRGSCFoptions.h contains the definitions of the DMRGSCFoptions container class.

CheMPS2/include/chemps2/DMRGSCFrotations.h contains the definitions of the DMRGSCFrotations class.

CheMPS2/include/chemps2/DMRGSCFunitary.h contains the definitions of the DMRGSCFunitary class.

CheMPS2/include/chemps2/DMRGSCFwtilde.h contains the definitions of the DMRGSCFwtilde class.

CheMPS2/include/chemps2/EdmistonRuedenberg.h contains the definitions of the EdmistonRuedenberg class.

CheMPS2/include/chemps2/Excitation.h contains the definitions of the Excitation class.

CheMPS2/include/chemps2/FCI.h contains the definitions of the FCI class.

CheMPS2/include/chemps2/FourIndex.h contains the definitions of the FourIndex class.

CheMPS2/include/chemps2/Hamiltonian.h contains the definitions of the Hamiltonian class.

CheMPS2/include/chemps2/Heff.h contains the definitions of the Heff class.

CheMPS2/include/chemps2/Initialize.h contains the definitions of the Initialize class.

CheMPS2/include/chemps2/Irreps.h contains the definitions of the Irreps class.

CheMPS2/include/chemps2/Lapack.h contains the definitions of the external BLAS and LAPACK routines.

CheMPS2/include/chemps2/Molden.h contains the definitions of the Molden class.

CheMPS2/include/chemps2/MPIchemps2.h contains the distribution of (complementary) renormalized operators over MPI processes, as well as wrappers for the MPI communication routines in the C API.

CheMPS2/include/chemps2/MyHDF5.h forces the use of the HDF5 1.8 API, e.g. H5Gcreate2 instead of H5Gcreate1, a known issue in Ubuntu 12.04.

CheMPS2/include/chemps2/Options.h contains all the options of the CheMPS2 namespace. Here the checkpoint storage names and folders can be set, as well as parameters related to memory usage and convergence.

CheMPS2/include/chemps2/Problem.h contains the definitions of the Problem class.

CheMPS2/include/chemps2/Sobject.h contains the definitions of the Sobject class.

CheMPS2/include/chemps2/Special.h contains special functions needed in various parts of libchemps2.

CheMPS2/include/chemps2/SyBookkeeper.h contains the definitions of the SyBookkeeper class.

CheMPS2/include/chemps2/Tensor3RDM.h contains the definitions of the Tensor3RDM class.

CheMPS2/include/chemps2/TensorF0.h contains the definitions of the TensorF0 class.

CheMPS2/include/chemps2/TensorF1.h contains the definitions of the TensorF1 class.

CheMPS2/include/chemps2/TensorGYZ.h contains the definitions of the TensorGYZ class.

CheMPS2/include/chemps2/Tensor.h contains the definitions of the virtual Tensor class.

CheMPS2/include/chemps2/TensorKM.h contains the definitions of the TensorKM class.

CheMPS2/include/chemps2/TensorL.h contains the definitions of the TensorL class.

CheMPS2/include/chemps2/TensorO.h contains the definitions of the TensorO class.

CheMPS2/include/chemps2/TensorOperator.h contains the definitions of the TensorOperator class.

CheMPS2/include/chemps2/TensorQ.h contains the definitions of the TensorQ class.

CheMPS2/include/chemps2/TensorS0.h contains the definitions of the TensorS0 class.

CheMPS2/include/chemps2/TensorS1.h contains the definitions of the TensorS1 class.

CheMPS2/include/chemps2/TensorT.h contains the definitions of the TensorT class.

CheMPS2/include/chemps2/TensorX.h contains the definitions of the TensorX class.

CheMPS2/include/chemps2/ThreeDM.h contains the definitions of the ThreeDM class.

CheMPS2/include/chemps2/TwoDM.h contains the definitions of the TwoDM class.

CheMPS2/include/chemps2/TwoIndex.h contains the definitions of the TwoIndex class.

CheMPS2/include/chemps2/Wigner.h contains the definitions of the Wigner class.

Please note that these files are documented with doxygen comments. The doxygen html output can be consulted online.

List of files to perform test runs

tests/test1.cpp.in contains several DMRG ground state calculations in different symmetry sectors for the N2 molecule (d2h symmetry) in the minimal STO-3G basis set.

tests/test2.cpp.in contains a ground state DMRG calculation of the ^1A1 state of H2O (c2v symmetry) in the 6-31G basis set.

tests/test3.cpp.in contains a ground state DMRG calculation of the ^1A1 state of CH4 (c2v symmetry) in the STO-3G basis set.

tests/test4.cpp.in contains a ground state DMRG calculation of the ^6A state of a linear Hubbard chain (forced c1 symmetry) with 10 sites and open boundary conditions, containing 9 fermions (just below half-filling).

tests/test5.cpp.in contains an excited state DMRG calculation in the ^1Ag symmetry sector of N2 (d2h symmetry) in the minimal STO-3G basis set. The ground and two lowest excited states are determined.

tests/test6.cpp.in contains a state-averaged DMRG-SCF calculation of the first excited state of the ^1Ag sector of O2 (d2h symmetry) in the CC-pVDZ basis set. The two 1s core orbitals are kept doubly occupied, and two Ag, B2g, B3g, B1u, B2u, and B3u orbitals are chosen as active space. A significant speedup is obtained with DIIS.

tests/test7.cpp.in reads in tests/matrixelements/O2.CCPVDZ.FCIDUMP, stores these matrix elements to disk, reads them back in from disk, and compares the two versions.

tests/test8.cpp.in contains a DMRG-SCF ground state calculation of the ^1Ag state of N2 (d2h symmetry) in the CC-pVDZ basis set. The two 1s core orbitals are kept doubly occupied. The next two Ag and B1u orbitals (sigma bonding and antibonding), as well as one B2g, B3g, B2u, and B3u orbital (pi bonding and antibonding) are chosen as active space. A significant speedup is obtained with DIIS. This test is smaller than test6, and is included for debugging with valgrind.

tests/test9.cpp.in contains a ground state DMRG calculation of a half-filled square 3 by 3 Hubbard lattice, both in the site basis and in the momentum basis. For the latter, the matrix elements only have fourfold permutation symmetry.

tests/test10.cpp.in is a copy of tests/test3.cpp.in, in which the FCI and DMRG 2- and 3-RDM are compared. This test also shows that after calculating the 2- and/or 3-RDM, it is possible to continue sweeping.

tests/test11.cpp.in is a copy of tests/test4.cpp.in, in which the FCI and DMRG 2- and 3-RDM are compared for a wavefunction with higher multiplicity.

tests/test12.cpp.in contains a ground state DMRG calculation of a BCS Hamiltonian. The matrix elements only have fourfold permutation symmetry.

tests/test13.cpp.in is a copy of the CASSCF calculation in tests/test8.cpp.in, but with full configuration interaction (FCI) as active space solver. In addition, the CASPT2 variational second order perturbation correction energy is calculated.

tests/test14.cpp.in is a copy of the CASSCF calculation in tests/test8.cpp.in with a slightly larger active space, and which works with ordered localized orbitals instead of natural orbitals. The localization occurs by means of Edmiston-Ruedenberg, and the ordering based on the Fiedler vector of the exchange matrix. In addition a calculation of the CASPT2 variational second order perturbation correction energy in the localized (i.e. not pseudocanonical) basis is performed.

tests/matrixelements/CH4.STO3G.FCIDUMP contains the matrix elements for test3 and test10.

tests/matrixelements/H2O.631G.FCIDUMP contains the matrix elements for test2.

tests/matrixelements/N2.STO3G.FCIDUMP contains the matrix elements for test1 and test5.

tests/matrixelements/O2.CCPVDZ.FCIDUMP contains the matrix elements for test6 and test7.

tests/matrixelements/N2.CCPVDZ.FCIDUMP contains the matrix elements for test8, test13, and test14.

The python tests in PyCheMPS2/tests/ are an identical conversion of the c++ tests.

These test files illustrate how to use libchemps2. Note that the tests are too small to see (near) linear scaling with the number of cores, although improvement should still be noticeable.