Search results for "Coupled"
showing 10 items of 742 documents
Anharmonic force fields from analytic CCSD(T) second derivatives: HOF and F2O
1999
The recent implementation of analytic second derivatives for CCSD(T) (coupled cluster theory with single and double excitations augmented by a perturbational treatment of connected triple excitations) has been combined with a numerical finite difference procedure to calculate cubic and semidiagonal quartic force fields. Computational details of this approach are outlined. Applications are reported for HOF and F2O. The CCSD(T) results are in excellent agreement with experiment and represent a substantial improvement over the results obtained from MP2 (Mo/ller–Plesset second-order perturbation theory).
Analytic gradients for Mukherjee’s multireference coupled-cluster method using two-configurational self-consistent-field orbitals
2010
Analytic gradients for the state-specific multireference coupled-cluster method suggested by Mahapatra et al. [Mol. Phys. 94, 157 (1998)] (Mk-MRCC) are reported within the singles and doubles approximation using two-configurational self-consistent field (TCSCF) orbitals. The present implementation extends our previous work on Mk-MRCC gradients [E. Prochnow et al., J. Chem. Phys. 131, 064109 (2009)] which is based on restricted Hartree-Fock orbitals and consequently the main focus of the present paper is on the treatment of orbital relaxation at the TCSCF level using coupled-perturbed TCSCF theory. Geometry optimizations on m-arynes and nitrenes are presented to illustrate the influence of t…
Pilot applications of internally contracted multireference coupled cluster theory, and how to choose the cluster operator properly.
2011
The internally contracted multireference coupled cluster (icMRCC) method allows a highly accurate description of both static and dynamic correlation with a computational scaling similar to single reference coupled cluster theory. The authors show that the method can lose its orbital invariance and size consistency when no special care is taken in the elimination of redundant excitations. Using the BeH(2) model system, four schemes are compared which differ in their treatment of linear dependencies between excitations of different rank (such as between singles and doubles). While the energy curves agree within tens of μE(h) when truncating the cluster operator at double excitations (icMRCCSD…
The body-mind problem from a personality relativity theory approach: (Relativity of personality)
2012
The body-mind problem is here posed fromthe General Factor of Personality Theory and mathematically presented as a relativity theory: 1. A two-level-invariant model; 2. The transformation equation between both levels. On a hand, the investigation of personality dynamicsas a consequenceof a stimulant drug provides a system of two coupled differential equations, which adapts to both biological (body) and psychological (mind)levels ofdescription. On the other hand, a system of two coupled partial differential equations is here deduced as the transformation model between the biological and psychological levels. Both models are presented and validated in this paper. The experimental design to va…
Analytically solvable 2×2 PT -symmetry dynamics from su(1,1)-symmetry problems ANALYTICALLY SOLVABLE 2×2 PT- SYMMETRY ... R. GRIMAUDO et al.
2019
A protocol for explicitly constructing the exact time-evolution operators generated by 2×2 time-dependent PT-symmetry Hamiltonians is reported. Its mathematical applicability is illustrated with the help of appropriate examples. The physical relevance of the proposed approach within gain-loss system scenarios, like two coupled waveguides, is discussed in detail.
Importance of Triples Contributions to NMR Spin–Spin Coupling Constants Computed at the CC3 and CCSDT Levels
2016
We present the first analytical implementation of CC3 second derivatives using the spin-unrestricted approach. This allows, for the first time, the calculation of nuclear spin–spin coupling constants (SSCC) relevant to NMR spectroscopy at the CC3 level of theory in a fully analytical manner. CC3 results for the SSCCs of a number of small molecules and their fluorine substituted derivatives are compared with the corresponding coupled cluster singles and doubles (CCSD) results obtained using specialized basis sets. For one-bond couplings the change when going from CCSD to CC3 is typically 1–3%, but much higher corrections were found for 1JCN in FCN, 15.7%, and 1JOF in OF2, 6.4%. The changes v…
Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes.
2014
A theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis- and trans-1,2-difluoroethylenes is reported. The results obtained using density functional theory (DFT) combined with large basis sets and gauge-independent atomic orbital calculations were critically compared with experiment and conventional, higher level correlated electronic structure methods. Accurate structural, vibrational, and NMR parameters of difluoroethylenes were obtained using several density functionals combined with dedicated basis sets. B3LYP/6-311++G(3df,2pd) optimized structures of difluoroethylenes closely reproduced experimental geometries and earlier reported b…
Orbital instabilities and spin-symmetry breaking in coupled-cluster calculations of indirect nuclear spin–spin coupling constants
2009
Abstract The effect of orbital instabilities is investigated for spin-symmetry breaking perturbations, namely the Fermi-contact (FC) and spin–dipole (SD) contributions to the indirect nuclear spin–spin coupling constants. For the CO and N 2 molecules the FC and SD contributions have been calculated and orbital-stability analyses for various interatomic distances have been carried out. This includes calculations at the Hartree–Fock self-consistent field (HF-SCF), coupled-cluster (CC) singles and doubles (CCSD), CC3, CCSD(T), CCSDT-4, CC singles, doubles, and triples (CCSDT) levels, and for the first time also at the CC singles, doubles, triples, and quadruples (CCSDTQ) level of theory. For c…
Full configuration-interaction and coupled-cluster calculations of the indirect spin–spin coupling constant of BH
2003
Abstract Full configuration-interaction calculations of the indirect spin–spin coupling constant of the BH molecule have been carried out in order to investigate the performance of various coupled-cluster (CC) methods in the treatment of electron-correlation effects, while the corresponding basis set convergence is analyzed in CC singles and doubles calculations. Assuming additivity of correlation and basis set effects, a theoretical estimate of 50.67 Hz is obtained for the 11 B 1 H spin–spin coupling constant.
Spin-orbit coupling constants from coupled-cluster response theory
2000
A scheme for the calculation of spin-orbit coupling constants using coupled-cluster (CC) electronic structure methods is described based on response-theory expressions for transition properties. An implementation is reported for singlet–triplet transitions within the coupled-cluster singles and doubles (CCSD) approximation. An atomic mean-field representation of the spin-orbit interaction is used to simplify the calculation of spin-orbit coupling constants. Sample calculations are presented for spin-orbit couplings for the 11Σ+→13Π transitions for BH and AlH and for the 11A′→13A″ and the 13A″→11A″ transitions for the silylenes HSiX, X=F, Cl, Br, and are compared to results obtained from ful…