Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    New type of noniterative energy corrections for excited electronic states: Extension of the method of moments of coupled-cluster equations to the equation-of-motion coupled-cluster formalism (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2966-2978 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed method of moments of coupled-cluster equations (MMCC) is extended to excited states via the equation-of-motion coupled-cluster (EOMCC) formalism. The main idea of the new MMCC theory is that of the noniterative energy corrections which, when added to the excited-state energies obtained in standard approximate EOMCC calculations, recover the exact energies. The MMCC corrections are expressed in terms of the generalized moments of the EOMCC equations. Approximate variants of the excited-state MMCC formalism, including the MMCC(2,3) approach, are introduced. In the MMCC(2,3) method, very simple energy corrections, expressed in terms of matrix elements of the triples-reference, triples-singles, and triples-doubles blocks of the EOMCCSD (EOMCC singles and doubles) similarity-transformed Hamiltonian, are added to the excited-state energies obtained in EOMCCSD calculations. The performance of the MMCC(2,3) approach is illustrated by the results of pilot calculations for the potential energy curves of ground and excited states of CH+. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1386794
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    The active-space equation-of-motion coupled-cluster methods for excited electronic states: Full EOMCCSDt (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 643-651 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The full version of the equation-of-motion coupled-cluster (EOMCC) method with all singles and doubles, and a selected set of triples defined through active orbitals (EOMCCSDt) has been implemented and tested using the H8, H2O, N2, C2, and CH+ systems. It is demonstrated that the full EOMCCSDt method provides the results of the full EOMCCSDT (EOMCC singles, doubles, and triples) quality at the fraction of the computer effort associated with the EOMCCSDT calculations. This includes excited states that are dominated by doubles and states that have large triexcited components. The excellent performance of the EOMCCSDt approach is observed even when the ground electronic state has a quasidegenerate character, which means that we can apply the EOMCCSDt formalism to excited states that cannot be adequately described by the perturbative triples models. The EOMCCSDt method is equivalent to the EOMCCSDT approach if all orbitals used in the EOMCCSDt calculations are active. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1378323
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Can ordinary single-reference coupled-cluster methods describe potential energy surfaces with nearly spectroscopic accuracy? The renormalized coupled-cluster study of the vibrational spectrum of HF (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5796-5804 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed renormalized (R) and completely renormalized (CR) CCSD(T) and CCSD(TQ) methods, which remove the failing of the standard CCSD(T) and CCSD(TQf) approaches at large internuclear separations, have been used to obtain the potential energy function and the vibrational spectrum of the HF molecule. The vibrational term values obtained in the renormalized and completely renormalized CCSD(T) and CCSD(TQ) calculations have been found to be in a better agreement with the experimental [Rydberg–Klein–Rees (RKR)] data than than the results of the expensive full CCSDT calculations. The simple R-CCSD(T) method gives 〈10 cm−1 errors for the vibrational energies up to ∼41 000 cm−1. The CR-CCSD(T) and CR-CCSD(TQ) methods reduce the ∼300 cm−1 errors in the full CCSDT results for the high-lying states near dissociation to 100–200 cm−1. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1400140
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The active-space equation-of-motion coupled-cluster methods for excited electronic states: The EOMCCSDt approach (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8490-8502 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The idea of selecting the most important higher-than-doubly excited configurations in single-reference coupled-cluster (CC) calculations for quasidegenerate ground states of molecular systems through the use of active orbitals is extended to excited electronic states via the equation-of-motion (EOM) CC formalism. The resulting EOMCCSDt method, in which triexcited clusters T3 and the corresponding three-body components of the EOMCC excitation operator R are restricted to internal and semiinternal components defined through active orbitals, is capable of significantly improving the vertical excitation energies obtained with the conventional EOMCCSD (EOMCC singles and doubles) approach at a fraction of the computer cost associated with the full EOMCCSDT (EOMCC singles, doubles, and triples) calculations. The results of pilot calculations for the H8, CH2, and CH+ molecules indicate that the EOMCCSDt method using small active spaces is as accurate as the EOMCCSDT approach. In particular, the EOMCCSDt method is capable of accurately describing states that are doubly excited relative to the reference state. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318757
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The method of moments of coupled-cluster equations and the renormalized CCSD[T], CCSD(T), CCSD(TQ), and CCSDT(Q) approaches (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 18-35 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper is the first in a series of papers on the new approach to the many-electron correlation problem, termed the method of moments of coupled-cluster equations (MMCC). A hierarchy of MMCC approximations, including the renormalized and completely renormalized CCSD[T], CCSD(T), CCSD(TQ), and CCSDT(Q) methods, which can be viewed as generalizations of the well-known perturbative coupled-cluster CCSD[T], CCSD(T), CCSD(TQf), and CCSDT(Qf) schemes, is introduced. In this initial study, an emphasis is placed on the ability of the MMCC approach to describe bond breaking and large effects due to connected triples and quadruples by modifying the standard noniterative CC approaches, such as the popular CCSD(T) method. The performance of selected MMCC approaches, including the renormalized and completely renormalized CCSD[T], CCSD(T), and CCSD(TQ) schemes, is illustrated by the results of pilot calculations for the HF and H2O molecules. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481769
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Renormalized coupled-cluster calculations of reactive potential energy surfaces: A comparison of the CCSD(T), renormalized CCSD(T), and full configuration interaction results for the collinear BeFH system (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 3617-3624 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed renormalized (R) and completely renormalized (CR) coupled-cluster singles, doubles, and noniterative triples (CCSD(T)) methods have been used to calculate the ground-state potential energy surface (PES) for the collinear BeFH system corresponding to the Be+HF→BeF+H reaction. It has been demonstrated that the ground-state PES obtained in the CR-CCSD(T) calculations is in perfect agreement with the exact PES obtained in the full configuration interaction calculations, whereas the PES resulting from the standard CCSD(T) calculations is qualitatively incorrect. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1494797
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Extension of the method of moments of coupled-cluster equations to excited states: The triples and quadruples corrections to the equation-of-motion coupled-cluster singles and doubles energies (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7411-7423 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed extension of the method of moments of coupled-cluster equations (MMCC) to excited states via the equation-of-motion coupled-cluster (EOMCC) formalism [K. Kowalski and P. Piecuch, J. Chem. Phys. 115, 2966 (2001)] is developed further. A new approximate variant of the excited-state MMCC theory, termed the MMCC(2,4) method, is proposed and tested. In the MMCC(2,4) method, relatively simple noniterative corrections due to triples and quadruples are added to the excited-state energies obtained in the standard EOMCCSD (EOMCC singles and doubles) calculations. The performance of the MMCC(2,4) approach is illustrated by the results of calculations for the excited states of N2, C2, and CH+. The MMCC(2,4) energies are compared with the results of the MMCC(2,3) calculations, in which noniterative corrections due to triples only are added to the EOMCCSD energies, and with the results of other EOMCC calculations, including various EOMCC triples schemes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1465407
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Renormalized CCSD(T) and CCSD(TQ) approaches: Dissociation of the N2 triple bond (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5644-5652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently proposed renormalized and completely renormalized CCSD(T) and CCSD(TQ) methods, which can be viewed as generalizations of the noniterative perturbative CCSD(T) and CCSD(TQf) schemes and which result from the more general method of moments of coupled-cluster equations, are applied to the dissociation of the ground-state N2 molecule. It is shown that the renormalized and completely renormalized CCSD(T) and CCSD(TQ) methods provide significantly better results for large N–N separations than their unrenormalized CCSD(T) and CCSD(TQf) counterparts. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290609
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    State-selective multireference coupled-cluster theory employing the single-reference formalism: Implementation and application to the H8 model system (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5792-5809 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The new state-selective (SS) multireference (MR) coupled-cluster (CC) method exploiting the single-reference (SR) particle-hole formalism, which we have introduced in our recent paper [P. Piecuch, N. Oliphant, and L. Adamowicz, J. Chem. Phys. 99, 1875 (1993)], has been implemented and the results of the pilot calculations for the minimum basis-set (MBS) model composed of eight hydrogen atoms in various geometrical arrangements are presented. This model enables a continuous transition between degenerate and nondegenerate regimes. Comparison is made with the results of SR CC calculations involving double (CCD), single and double (CCSD), single, double, and triple (CCSDT), and single, double, triple, and quadruple (CCSDTQ) excitations. Our SS CC energies are also compared with the results of the Hilbert space, state-universal (SU) MR CC(S)D calculations, as well as with the MR configuration interaction (CI) results (with and without Davidson-type corrections) and the exact correlation energies obtained using the full CI (FCI) method. Along with the ground-state energies, we also analyze the resulting wave functions by examining some selected cluster components. This analysis enables us to assess the quality of the resulting wave functions. Our SS CC theory truncated at double excitations, which emerges through selection of the most essential clusters appearing in the full SR CCSDTQ formalism [SS CCSD (TQ) method] provides equally good results in nondegenerate and quasidegenerate regions. The difference between the ground-state energy obtained with the SS CCSD(TQ) approach and the FCI energy does not exceed 1.1 mhartree over all the geometries considered. This value compares favorably with the maximum difference of 2.8 mhartree between the SU CCSD energies and the FCI energies obtained for the same range of geometries. The SS CCSD(T) method, emerging from the SR CCSDT theory through selection of the most essential clusters, is less stable, since it neglects very important semi-internal quadruple excitations. Unlike the genuine multideterminantal SU CC formalism, our SS CC approach is not affected by the intruder state problem and its convergence remains satisfactory in nondegenerate and quasidegenerate regimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467143
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    State-selective multi-reference coupled-cluster theory employing the single-reference formalism: Application to an excited state of H8 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3301-3306 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-selective (SS) multi-reference (MR) coupled-cluster (CC) method exploiting the single-reference (SR) formalism [P. Piecuch, N. Oliphant, and L. Adamowicz, J. Chem. Phys. 99, 1875 (1993)] is applied to the first excited totally symmetric singlet state of a prototype molecular system composed of eight hydrogen atoms. Minimum basis set is employed and various geometries are considered. The SS CC energies are compared with the results of the state-universal (SU) MR CC calculations involving single and double excitations (CCSD) as well as with the exact energies obtained using the full configuration interaction method. Comparison is also made with the results of the standard SR CCSD calculations. In both nondegenerate and quasidegenerate regions, our SS CC theory truncated at double excitations [SS CCSD(TQ) method] provides much better description of the first excited state than the genuine multi-determinantal SU CCSD formalism. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468641
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...