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Hans Lischka - One of the best experts on this subject based on the ideXlab platform.
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a Multireference Configuration Interaction study of the photodynamics of nitroethylene
Journal of Physical Chemistry A, 2014Co-Authors: Itamar Borges, Hans Lischka, Adelia J A AquinoAbstract:Extended Multireference Configuration Interaction with singles and doubles (MR-CISD) calculations of nitroethylene (H2C═CHNO2) were carried out to investigate the photodynamical deactivation paths to the ground state. The ground (S0) and the first five valence excited electronic states (S1–S5) were investigated. In the first step, vertical excitations and potential energy curves for CH2 and NO2 torsions and CH2 out-of-plane bending starting from the ground state geometry were computed. Afterward, five conical intersections, one between each pair of adjacent states, were located. The vertical calculations mostly confirm the previous assignment of experimental spectrum and theoretical results using lower-level calculations. The conical intersections have as main features the torsion of the CH2 moiety, different distortions of the NO2 group and CC, CN, and NO bond stretchings. In these conical intersections, the NO2 group plays an important role, also seen in excited state investigations of other nitro molec...
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new implementation of the graphical unitary group approach for Multireference direct Configuration Interaction calculations
International Journal of Quantum Chemistry, 2009Co-Authors: Hans Lischka, Ron Shepard, Franklin B Brown, Isaiah ShavittAbstract:Improved procedures were used in a new computer implementation of the graphical unitary group approach, designed specifically for efficient Multireference Configuration Interaction calculations for molecules. These procedures include improvements in the treatment of spatial symmetry and of the Multireference interacting space, and include the “repartitioned Hamiltonian,” which provides a flexible alternative to conventional particle-hole formalisms. The new computer programs avoid the construction of very long formula files, and leave the matrix eigenvector iterations as the only significant rate-determining step in large-scale direct CI calculations.
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a Multireference Configuration Interaction investigation of the excited state energy surfaces of fluoroethylene c2h3f
Journal of Physical Chemistry A, 2005Co-Authors: Mario Barbatti, And Adelia Justina Aguiar Aquino, Hans LischkaAbstract:Multireference Configuration Interaction with singles and doubles (MR-CISD) calculations has been performed for the optimization of conical intersections and stationary points on the fluoroethylene excited-state energy surfaces. For the planar ground state geometry, the vertical spectrum including 3s and 3p Rydberg states was calculated. From this geometry, a rigid torsion around the CC bond strongly reduces the energy gap between S0 and S1 states. Furthermore, a search for the minimum of the crossing seam shows that there exists a conical intersection close to the twisted structure and two additional ones for cis and trans pyramidalized structures. These three intersections are connected by the same seam. We have shown that the Hula-Twist process is an alternative way to the direct CC twisting in order to reach this part of the seam. Other conical intersections were also located in the CH3CF and CH2FCH, H-migration, and C3v structures. The photodynamics of the system is discussed based on topological fea...
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photochemistry of ethylene a Multireference Configuration Interaction investigation of the excited state energy surfaces
Journal of Chemical Physics, 2004Co-Authors: Mario Barbatti, Joachim Paier, Hans LischkaAbstract:Multireference Configuration Interaction with singles and doubles (MR-CISD) calculations have been performed for the optimization of conical intersections and stationary points on the ethylene excited-state energy surfaces using recently developed methods for the computation of analytic gradients and nonadiabatic coupling terms. Basis set dependence and the effect of various choices of reference spaces for the MR-CISD calculations have been investigated. The crossing seam between the S0 and S1 states has been explored in detail. This seam connects all conical intersections presently known for ethylene. Major emphasis has been laid on the hydrogen-migration path. Starting in the V state of twisted-orthogonal ethylene, a barrierless path to ethylidene was found. The feasibility of ethylidene formation will be important for the explanation of the relative yield of cis and trans H2 elimination.
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geometry optimization of excited valence states of formaldehyde using analytical Multireference Configuration Interaction singles and doubles and Multireference averaged quadratic coupled cluster gradients and the conical intersection formed by the 1 1b1 σ π and 2 1a1 π π states
Journal of Chemical Physics, 2001Co-Authors: Michal Dallos, Hans Lischka, Thomas Muller, Ron ShepardAbstract:Extended MR-CISD (Multireference Configuration Interaction singles and doubles), MR-CISD+Q (Multireference Configuration Interaction singles, doubles, and quadrupole), and MR-AQCC (Multireference averaged quadratic coupled clusters) calculations have been performed on the following valence states of formaldehyde: 1 1A1 (planar ground state), 1 1A2 and 1 1A″ (planar and nonplanar n-π* state), 1 1B1 and 2 1A1 (planar σ-π* and π-π* states) and their nonplanar counterparts 2 1A′ and 3 1A′. Full geometry optimizations have been performed using analytic gradient techniques developed for the MR-CISD and MR-AQCC methods as implemented into the COLUMBUS program system. Basis set extrapolation techniques have been used for the determination of high-accuracy geometries and adiabatic excitation energies. Harmonic vibrational frequencies have been computed also. Agreement between calculated and available experimental data is very good. Especially for the σ-π* and π-π* states experimental information is extremely scarc...
Emily A Carter - One of the best experts on this subject based on the ideXlab platform.
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
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size extensivity corrected Multireference Configuration Interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons
Journal of Chemical Physics, 2014Co-Authors: Victor B Oyeyemi, David B Krisiloff, John A Keith, Florian Libisch, Michele Pavone, Emily A CarterAbstract:Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires Multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on Multireference Configuration Interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from Multireference singles and doubles Configuration Interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.
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size extensive modification of local Multireference Configuration Interaction
Journal of Chemical Physics, 2004Co-Authors: Arun Venkatnathan, Andrew B Szilva, Derek Walter, Robert J Gdanitz, Emily A CarterAbstract:We recently developed a reduced scaling Multireference Configuration Interaction (MRCI) method based on local correlation in the internal (occupied) and external (virtual) orbital spaces. This technique can be used, e.g., to predict bond dissociation energies in large molecules with reasonable accuracy. However, the inherent lack of size extensivity of truncated CI is a disadvantage that in principle worsens as the system size grows. Here we implement an a priori size-extensive modification of local MRCI known as the averaged coupled pair functional (ACPF) method. We demonstrate that local MR-ACPF recovers more correlation energy than local MRCI, in keeping with trends observed previously for nonlocal ACPF. We test the size extensivity of local ACPF on noninteracting He atoms and a series of hydrocarbons. Basis set and core correlation effects are explored, as well as bond breaking in a variety of organic molecules. The local MR-ACPF method proves to be a useful tool for investigating large molecules and represents a further improvement in predictive accuracy over local MRCI.
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local weak pairs pseudospectral Multireference Configuration Interaction
Journal of Chemical Physics, 2002Co-Authors: Derek Walter, Andrew B Szilva, Keith Niedfeldt, Emily A CarterAbstract:We present a new reduced scaling Multireference singles and doubles Configuration Interaction (MRSDCI) algorithm based upon the combination of local correlation and pseudospectral methods. Taking advantage of the locality of the Coulomb potential, the weak-pairs approximation of Saebo/ and Pulay is employed to eliminate Configurations having simultaneous excitations out of pairs of distant, weakly interacting orbitals. In conjunction with this, the pseudospectral approximation is used to break down the most time-consuming two-electron integrals into a product of intermediate quantities depending on no more than two orbital indices. The resulting intermediate quantities are then used directly in the CI equations to substantially reduce the number of floating point operations required for diagonalization of the Hamiltonian. Additionally, our CI algorithm is based upon the symmetric group graphical approach CI (SGGA-CI) of Duch and Karwowski. For the purpose of developing reduced scaling CI algorithms, this approach has some important advantages. The most important of these advantages are the on-the-fly calculation of integral coupling coefficients and the separation of the spin and spatial parts of the wave function, which simplifies implementation of local correlation approximations. We apply the method to determine a series of binding energies in hydrocarbons and show that the approximate method predicts binding energies that are within a few kcal/mol of those predicted by the analytic nonlocal method. For large molecules, the local pseudospectral method was shown to be over 7 times as fast as the analytic nonlocal method. We also carry out a systematic study on the performance of different basis sets in the weak-pairs method. It was determined that triple-ζ basis sets were capable of recovering only 99.0% of the correlation energy, whereas double-ζ basis sets recovered 99.9% of the correlation energy.
Theresa L Windus - One of the best experts on this subject based on the ideXlab platform.
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
Takeshi Yanai - One of the best experts on this subject based on the ideXlab platform.
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fully internally contracted Multireference Configuration Interaction theory using density matrix renormalization group a reduced scaling implementation derived by computer aided tensor factorization
Journal of Chemical Theory and Computation, 2015Co-Authors: Masaaki Saitow, Yuki Kurashige, Takeshi YanaiAbstract:We present an extended implementation of the Multireference Configuration Interaction (MRCI) method combined with the quantum-chemical density matrix renormalization group (DMRG). In the previous study, we introduced the combined theory, referred to as DMRGMRCI, as a method to calculate high-level dynamic electron correlation on top of the DMRG wave function that accounts for active-space (or strong) correlation using a large number of active orbitals. The DMRG-MRCI method is built on the full internal-contraction scheme for the compact reference treatment and on the cumulant approximation for the treatment of the four-particle rank reduced density matrix (4-RDM). The previous implementation achieved the MRCI calculations with the active space (24e,24o), which are deemed the record largest, whereas the inherent Nact 8 × N complexity of computation was found a hindrance to using further large active space. In this study, an extended optimization of the tensor contractions is developed by explicitly incorporating the rank reduction of the decomposed form of the cumulant-approximated 4-RDM into the factorization. It reduces the computational scaling (to Nact7 × N) as well as the cache-miss penalty associated with direct evaluation of complex cumulant reconstruction. The present scheme, however, faces the increased complexity of factorization patterns for optimally implementing the tensor contraction terms involving the decomposed 4-RDM objects. We address this complexity using the enhanced symbolic manipulation computer program for deriving and coding programmable equations. The new DMRG-MRCI implementation is applied to the determination of the stability of the iron(IV)-oxo porphyrin relative to the iron(V) electronic isomer (electromer) using the active space (29e,29o) (including four second d-shell orbitals of iron) with triple-ζ-quality atomic orbital basis sets. The DMRG-cu(4)-MRCI+Q model is shown to favor the triradicaloid iron(IV)-oxo state as the lowest energy state and characterize the iron(V) electromer as thermally inaccessible, supporting the earlier experimental and density functional studies. This conflicts with the previous MR calculations using the restricted activespace second-order perturbation theory (RASPT2) with the similar-size active space (29e,28o) reported by Pierloot et al. (Radon, M.; Broclawik, E.; Pierloot, K. J. Chem. Theory Comput. 2011, 7, 898), showing that the hypothetical iron(V) state indicated by recent laser flash photolysis (LFP) studies is likely thermally accessible because of its underestimated relative energy.
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Multireference Configuration Interaction theory using cumulant reconstruction with internal contraction of density matrix renormalization group wave function
Journal of Chemical Physics, 2013Co-Authors: Masaaki Saitow, Yuki Kurashige, Takeshi YanaiAbstract:We report development of the Multireference Configuration Interaction (MRCI) method that can use active space scalable to much larger size references than has previously been possible. The recent development of the density matrix renormalization group (DMRG) method in Multireference quantum chemistry offers the ability to describe static correlation in a large active space. The present MRCI method provides a critical correction to the DMRG reference by including high-level dynamic correlation through the CI treatment. When the DMRG and MRCI theories are combined (DMRG-MRCI), the full internal contraction of the reference in the MRCI ansatz, including contraction of semi-internal states, plays a central role. However, it is thought to involve formidable complexity because of the presence of the five-particle rank reduced-density matrix (RDM) in the Hamiltonian matrix elements. To address this complexity, we express the Hamiltonian matrix using commutators, which allows the five-particle rank RDM to be canc...
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Multireference Configuration Interaction theory using cumulant reconstruction with internal contraction of density matrix renormalization group wave function
Journal of Chemical Physics, 2013Co-Authors: Masaaki Saitow, Yuki Kurashige, Takeshi YanaiAbstract:We report development of the Multireference Configuration Interaction (MRCI) method that can use active space scalable to much larger size references than has previously been possible. The recent development of the density matrix renormalization group (DMRG) method in Multireference quantum chemistry offers the ability to describe static correlation in a large active space. The present MRCI method provides a critical correction to the DMRG reference by including high-level dynamic correlation through the CI treatment. When the DMRG and MRCI theories are combined (DMRG-MRCI), the full internal contraction of the reference in the MRCI ansatz, including contraction of semi-internal states, plays a central role. However, it is thought to involve formidable complexity because of the presence of the five-particle rank reduced-density matrix (RDM) in the Hamiltonian matrix elements. To address this complexity, we express the Hamiltonian matrix using commutators, which allows the five-particle rank RDM to be canceled out without any approximation. Then we introduce an approximation to the four-particle rank RDM by using a cumulant reconstruction from lower-particle rank RDMs. A computer-aided approach is employed to derive the exceedingly complex equations of the MRCI in tensor-contracted form and to implement them into an efficient parallel computer code. This approach extends to the size-consistency-corrected variants of MRCI, such as the MRCI+Q, MR-ACPF, and MR-AQCC methods. We demonstrate the capability of the DMRG-MRCI method in several benchmark applications, including the evaluation of single-triplet gap of free-base porphyrin using 24 active orbitals.
Luke Roskop - One of the best experts on this subject based on the ideXlab platform.
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
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spin free 2 r12 basis set incompleteness correction to the local Multireference Configuration Interaction and the local Multireference average coupled pair functional methods
Journal of Chemical Theory and Computation, 2016Co-Authors: Luke Roskop, Emily A Carter, Edward F Valeev, Mark S Gordon, Theresa L WindusAbstract:The local Multireference Configuration Interaction (LMRCI) and local Multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]R12/LMRCI+Q+[2]R12/LMRACPF+[2]R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q).
