The goal of this paper is to examine the performance of the conventional and renormalized single-reference coupled-cluster (CC) methods in calculations of the potential energy surface of the water molecule. A comparison with the results of the internally contracted multi-reference configuration interaction calculations including the quasi-degenerate Davidson correction (MRCI(Q)) and the spectroscopically accurate potential energy surface of water resulting from the use of the energy switching (ES) approach indicates that the relatively inexpensive completely renormalized (CR) CC methods with singles (S), doubles (D), and a non-iterative treatment of triples (T) or triples and quadruples (TQ), such as CR-CCSD(T), CR-CCSD(TQ), and the recently developed rigorously size extensive extension of CR-CCSD(T), termed CR-CC(2,3), provide substantial improvements in the results of conventional CCSD(T) and CCSD(TQ) calculations at larger internuclear separations. It is shown that the CR-CC(2,3) results corrected for the effect of quadruply excited clusters through the CR-CC(2,3)+Q approach can compete with the highly accurate MRCI(Q) data. The excellent agreement between the CR-CC(2,3)+Q and MRCI(Q) results suggests ways of improving the global potential energy surface of water resulting from the use of the ES approach in the regions of intermediate bond stretches and intermediate energies connecting the region of the global minimum with the asymptotic regions.

1 aZheng, J.1 aGour, J., R1 aLutz, J.J.1 aWloch, M.1 aPiecuch, Piotr1 aTruhlar, D.G. uhttps://icer.msu.edu/research/publications/application-renormalized-coupled-cluster-methods-potential-function-water02707nas a2200301 4500008004100000245017900041210006900220260001200289300001300301490000800314520164400322653003101966653003301997653002402030653001902054653001802073653001802091653001502109653002202124653002102146653003002167100001602197700001902213700001602232700001402248700001802262856012502280 2007 eng d00aActive-Space Symmetry-Adapted-Cluster Configuration-Interaction and Equation-of-Motion Cluster Methods for High Accuracy Calculations of Potential Energy Surfaces of Radicals0 aActiveSpace SymmetryAdaptedCluster ConfigurationInteraction and c04/2007 a28 pages0 v1263 aThe electron-attached (EA) and ionized (IP) symmetry-adapted-cluster configuration-interaction (SAC-CI) methods and their equation-of-motion coupled-cluster (EOMCC) analogs provide an elegant framework for studying open-shell systems. As shown in this study, these schemes require the presence of higher-order excitations, such as the four-particle-three-hole (4p-3h) or four-hole–three-particle (4h-3p) terms, in the electron attaching or ionizing operator R in order to produce accurate ground- and excited-state potential energy surfaces of radicals along bond breaking coordinates. The full inclusion of the 4p-3h/4h-3p excitations in the EA/IP SAC-CI and EOMCC methods leads to schemes which are far too expensive for calculations involving larger radicals and realistic basis sets. In order to reduce the large costs of such schemes without sacrificing accuracy, the active-space EA/IP EOMCC methodology [ J. R. Gour et al., J. Chem. Phys. 123, 134113 (2005) ] is extended to the EA/IP SAC-CI approaches with 4p-3h/4h-3p excitations. The resulting methods, which use a physically motivated set of active orbitals to pick out the most important 3p-2h/3h-2p and 4p-3h/4h-3p excitations, represent practical computational approaches for high-accuracy calculations of potential energy surfaces of radicals. To illustrate the potential offered by the active-space EA/IP SAC-CI approaches with up to 4p-3h/4h-3p excitations, the results of benchmark calculations for the potential energy surfaces of the low-lying doublet states of CH and OH are presented and compared with other SAC-CI and EOMCC methods, and full CI results.

10aconfiguration interactions10acoupled cluster calculations10aelectron attachment10aexcited states10afree radicals10aground states10aionisation10aorganic compounds10aoxygen compounds10apotential energy surfaces1 aOhtsuka, Y.1 aPiecuch, Piotr1 aGour, J., R1 aEhara, M.1 aNakatsuji, H. uhttps://icer.msu.edu/active-space-symmetry-adapted-cluster-configuration-interaction-and-equation-motion-cluster-methods01273nas a2200205 4500008004100000245008900041210006900130260001200199300001200211490000700223520060600230100001900836700001400855700001700869700001600886700002600902700001900928700001700947856010300964 2006 eng d00aAb Initio Coupled-Cluster Calculations for Nuclei Using Methods of Quantum Chemistry0 aAb Initio CoupledCluster Calculations for Nuclei Using Methods o c09/2005 a485-4880 v253 aWe report preliminary large scale ab initio calculations of ground and excited states of 16O using quantum chemistry inspired coupled cluster methods and realistic two-body interactions. By using the renormalized Hamiltonians obtained with a no-core G-matrix approach, we obtain the virtually converged results at the level of two-body interactions. Due to the polynomial scaling with the system size that characterizes coupled cluster methods, we can probe large model spaces with up to seven major oscillator shells, for which standard non-truncated shell-model calculations are not possible.

1 aPiecuch, Piotr1 aWloch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aPapenbrock, T.1 aKowalski, K. uhttps://icer.msu.edu/ab-initio-coupled-cluster-calculations-nuclei-using-methods-quantum-chemistry01862nas a2200181 4500008004100000245005700041210005600098260001200154300001400166490000800180520132100188100001501509700001901524700002001543700001801563700002401581856007501605 2006 eng d00aAb initio determination of solid-state nanostructure0 aAb initio determination of solidstate nanostructure c07/2005 a655–6580 v4403 aAdvances in materials science and molecular biology followed rapidly from the ability to characterize atomic structure using single crystals1, 2, 3, 4. Structure determination is more difficult if single crystals are not available5. Many complex inorganic materials that are of interest in nanotechnology have no periodic long-range order and so their structures cannot be solved using crystallographic methods6. Here we demonstrate that ab initio structure solution of these nanostructured materials is feasible using diffraction data in combination with distance geometry methods. Precise, sub-ångström resolution distance data are experimentally available from the atomic pair distribution function (PDF)6, 7. Current PDF analysis consists of structure refinement from reasonable initial structure guesses6, 7 and it is not clear, a priori, that sufficient information exists in the PDF to obtain a unique structural solution. Here we present and validate two algorithms for structure reconstruction from precise unassigned interatomic distances for a range of clusters. We then apply the algorithms to find a unique, ab initio, structural solution for C60 from PDF data alone. This opens the door to sub-ångström resolution structure solution of nanomaterials, even when crystallographic methods fail.

1 aJuhás, P.1 aCherba, D., M.1 aDuxbury, P., M.1 aPunch, W., F.1 aBillinge, S., J. L. uhttps://icer.msu.edu/ab-initio-determination-solid-state-nanostructure01812nas a2200169 4500008004100000245007100041210006900112260001200181300001100193490000700204520127500211100001901486700002001505700001701525700002301542856007701565 2006 eng d00aAb initio studies of the electronic structure of defects in {PbTe}0 aAb initio studies of the electronic structure of defects in PbTe c10/2006 a1552050 v743 aUnderstanding the detailed electronic structure of deep defect states in narrow band-gap semiconductors has been a challenging problem. Recently, self-consistent ab initio calculations within density functional theory using supercell models have been successful in tackling this problem. In this paper, we carry out such calculations in {PbTe,} a well-known narrow band-gap semiconductor, for a large class of defects: cationic and anionic substitutional impurities of different valence, and cationic and anionic vacancies. For the cationic defects, we study the chemical trends in the position of defect levels by looking at series of compounds {RPb2n−1Te2n,} where R is vacancy or monovalent, divalent, or trivalent atom. Similarly, for anionic defects, we study compounds {MPb2nTe2n−1,} where M is vacancy, S, Se or I. We find that the density of states near the top of the valence band and the bottom of the conduction band get significantly modified for most of these defects. This suggests that the transport properties of {PbTe} in the presence of impurities may not always be interpreted by simple carrier doping (from bound impurity states in the gap) concepts, confirming such ideas developed from qualitative and semiquantitative arguments.

1 aAhmad, Salameh1 aMahanti, S., D.1 aHoang, Khang1 aKanatzidis, M., G. uhttps://icer.msu.edu/ab-initio-studies-electronic-structure-defects-pbte01498nas a2200181 4500008004100000245011900041210006900160260001200229300001200241490000800253520084400261100001901105700001501124700001701139700001501156700002401171856012101195 2006 eng d00aAutomated derivation and parallel computer implementation of renormalized and active-space coupled-cluster methods0 aAutomated derivation and parallel computer implementation of ren c08/2005 a79–970 v1063 aOur recent efforts that have led to an automated derivation and computer implementation of the renormalized and active-space coupled-cluster {(CC)} methods with Tensor Contraction Engine {(TCE)} are summarized. The {TCE-generated} renormalized and active-space {CC} computer codes are parallel and applicable to closed- and open-shell references, enabling accurate calculations of potential energy surfaces along bond-breaking coordinates and excited states displaying a significant multi-reference character. The effectiveness of the new codes in describing electronic quasi-degeneracies is illustrated by the renormalized {CC} calculations of the potential energy curve of {HCl} and the active-space {CC} calculations for the low-lying excited states of the Be3 system. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

1 aPiecuch, Piotr1 aHirata, So1 aKowalski, K.1 aFan, P.-D.1 aWindus, Theresa, L. uhttps://icer.msu.edu/automated-derivation-and-parallel-computer-implementation-renormalized-and-active-space-coupled01260nas a2200205 4500008004100000245004300041210004200084260001200126300001100138490000700149520068900156100001500845700001700860700001600877700002600893700001700919700001900936700001600955856008300971 2005 eng d00aAb Initio Coupled-Cluster Study of 16O0 aAb Initio CoupledCluster Study of 16O c06/2005 a2125010 v943 aWe report converged results for the ground and excited states and matter density of 16O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and algorithms developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a one-particle, one-hole nature, but it cannot describe the first-excited 0+ state. Incorporation of triples has no effect on the latter finding.

1 aWłoch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aKowalski, K.1 aPapenbrock, T.1 aPiecuch, P. uhttps://icer.msu.edu/research/publications/ab-initio-coupled-cluster-study-16o01233nas a2200193 4500008004100000245004100041210004000082260001200122490000700134520068900141100001900830700001400849700001700863700001600880700002600896700001700922700001900939856008100958 2005 eng d00aAb Initio Coupled-Cluster Study of O0 aAb Initio CoupledCluster Study of O c06/20050 v943 aWe report converged results for the ground and excited states and matter density of 16O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and algorithms developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a one-particle, one-hole nature, but it cannot describe the first-excited 0+ state. Incorporation of triples has no effect on the latter finding.

1 aPiecuch, Piotr1 aWloch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aKowalski, K.1 aPapenbrock, T. uhttps://icer.msu.edu/research/publications/ab-initio-coupled-cluster-study-o01316nas a2200181 4500008004100000245006800041210006600109260001200175300001200187490000800199520074000207100001900947700001700966700001500983700001400998700001701012856010501029 2005 eng d00aActive-Space Coupled-Cluster Study of Electronic States of Be 30 aActiveSpace CoupledCluster Study of Electronic States of Be 3 c08/2005 a6 pages0 v1233 aThe active-space coupled-cluster (CC) and equation-of-motion (EOM) CC methods with all single and double excitations with triple excitations defined via active orbitals (CCSDt, EOMCCSDt), as implemented with TENSOR CONTRACTION ENGINE, are applied to the challenging Be3 system, which is characterized by a large number of low-lying excited states dominated by two-electron transitions and significant high-order correlation effects in the ground electronic state. It is demonstrated that the CCSDt and EOMCCSDt methods provide an excellent description of complicated electronic quasidegeneracies present in the Be3 cluster. Different strategies for defining triple excitations within the CCSDt∕EOMCCSDt approach are discussed.

1 aPiecuch, Piotr1 aKowalski, K.1 aHirata, S.1 aWloch, M.1 aWindus, T.L. uhttps://icer.msu.edu/research/publications/active-space-coupled-cluster-study-electronic-states-be-300613nas a2200145 4500008004100000245014900041210006900190260001200259300001300271490000800284100001900292700001600311700001400327856012600341 2005 eng d00aActive-Space Equation-of=Motion Coupled-Cluster Methods for Excited States of Radicals and Other Open-Shell Systems: EA-EOMCCSDt and IP-EOMCCSDt0 aActiveSpace EquationofMotion CoupledCluster Methods for Excited c10/2005 a14 pages0 v1231 aPiecuch, Piotr1 aGour, J., R1 aWloch, M. uhttps://icer.msu.edu/research/publications/active-space-equation-ofmotion-coupled-cluster-methods-excited-states-radicals01392nas a2200181 4500008004100000245015300041210006900194300001600263490000800279520065800287653003300945653001800978653003200996100002201028700001901050700001701069856012401086 2005 eng d00aActive-space equation-of-motion coupled-cluster methods for excited states of radicals and other open-shell systems: {EA-EOMCCSDt} and {IP-EOMCCSDt}0 aActivespace equationofmotion coupledcluster methods for excited a134113–140 v1233 aThe previously developed active-space coupled-cluster (CC) and equation-of-motion (EOM) CC methods are extended to radicals and other open-shell systems by combining them with the electron attached (EA) and ionized (IP) EOMCC approaches. As illustrated by the calculations for the CH and OH radicals, the resulting EA-EOMCCSDt and IP-EOMCCSDt theories are capable of providing a highly accurate description of the electronic spectra of radical systems, including excited states displaying a manifestly multideterminantal nature, with the low costs that are not much greater that those characterizing the standard EOMCC singles and doubles method.

10acoupled cluster calculations10afree radicals10amolecular electronic states1 aGour, Jeffrey, R.1 aPiecuch, Piotr1 aWloch, Marta uhttps://icer.msu.edu/research/publications/active-space-equation-motion-coupled-cluster-methods-excited-states-radicals