showing 28 related works from this author
Polarizability and optical rotation calculated from the approximate coupled cluster singles and doubles CC2 linear response theory using cholesky dec…
2004
A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model using Cholesky decomposition of the two-electron integrals is presented. Significantly reducing storage demands and computational effort without sacrificing accuracy compared to the conventional model, the algorithm is well suited for large-scale applications. Extensive basis set convergence studies are presented for the static and frequency-dependent electric dipole polarizability of benzene and C60, and for the optical rotation of CNOFH2 and (−)-trans-cyclooctene (TCO). The origin-dependence of the optical rotation is calculated and shown to persist for CC2 even at basis set convergence. …
The CCSD(T) model with Cholesky decomposition of orbital energy denominators
2010
A new implementation of the coupled cluster singles and doubles with approximate triples correction method [CCSD(T)] using Cholesky decomposition of the orbital energy denominators is described. The new algorithm reduces the scaling of CCSD(T) from N-7 to N-6, where N is the number of orbitals. The Cholesky decomposition is carried out using simple analytical expressions that allow us to evaluate a priori the order in which the decomposition should be carried out and to obtain the relevant parts of the vectors whenever needed in the calculation. Several benchmarks have been carried out comparing the performance of the conventional and Cholesky CCSD(T) implementations. The Cholesky implement…
Carbon nanorings: A challenge to theoretical chemistry
2006
High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions - caused by the polarization associated to curved Ï-conjugated systems - and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the …
Size-intensive decomposition of orbital energy denominators
2000
We introduce an alternative to Almlöf and Häser’s Laplace transform decomposition of orbital energy denominators used in obtaining reduced scaling algorithms in perturbation theory based methods. The new decomposition is based on the Cholesky decomposition of positive semidefinite matrices. We show that orbital denominators have a particular short and size-intensive Cholesky decomposition. The main advantage in using the Cholesky decomposition, besides the shorter expansion, is the systematic improvement of the results without the penalties encountered in the Laplace transform decomposition when changing the number of integration points in order to control the convergence. Applications will…
Origin invariant calculation of optical rotation without recourse to London orbitals
2004
We propose an inherently origin invariant formulation of specific optical rotation obtained from the conventional velocity gauge expression by subtracting the static limit from the electric dipole-magnetic dipole polarizability: ããpâ,LâããÏâããpâ,LâããÏ-ããpâ,Lâãã0. London (gauge including) atomic orbitals are therefore not needed to ensure origin invariance and, consequently, this modified velocity gauge formulation may be employed in conjunction with variational and non-variational quantum chemical methods alike. Sample calculations on S-propylene oxide and 3,4- methylenedioxymethamphetamine using self-consistent field and coupled cluster wave functions…
Method specific Cholesky decomposition : Coulomb and exchange energies
2008
We present a novel approach to the calculation of the Coulomb and exchange contributions to the total electronic energy in self consistent field and density functional theory. The numerical procedure is based on the Cholesky decomposition and involves decomposition of specific Hadamard product matrices that enter the energy expression. In this way, we determine an auxiliary basis and obtain a dramatic reduction in size as compared to the resolution of identity (RI) method. Although the auxiliary basis is determined from the energy expression, we have complete control of the errors in the gradient or Fock matrix. Another important advantage of this method specific Cholesky decomposition is t…
The Dalton quantum chemistry program system
2013
Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, confi ...
Calculation of size‐intensive transition moments from the coupled cluster singles and doubles linear response function
1994
Coupled cluster singles and doubles linear response (CCLR) calculations have been carried out for excitation energies and dipole transition strengths for the lowest excitations in LiH, CH+, and C4and the results compared with the results from a CI-like approach to equation of motion coupled cluster (EOMCC). The transition strengths are similar in the two approaches for single molecule calculations on small systems. However, the CCLR approach gives size-intensive dipole transition strengths, while title EOMCC formalism does not. Thus, EOMCC calculations can give unphysically dipole transition strengths, e.g., in EOMCC calculations on a sequence of noninteracting LiH systems we obtained a neg…
Cholesky decomposition-based definition of atomic subsystems in electronic structure calculations
2010
Decomposing the Hartree-Fock one-electron density matrix and a virtual pseudodensity matrix, we obtain an orthogonal set of normalized molecular orbitals with local character to be used in post-Hartree-Fock calculations. The applicability of the procedure is illustrated by calculating CCSD(T) energies and CCSD molecular properties in reduced active spaces. © 2010 American Institute of Physics.
A coupled cluster calculation of the spectrum of urea
2001
Several coupled cluster methods have been used to compute the vertical excitation energies and oscillator strengths of the lowest singlet states of urea. Except for one excitation, the results are in good agreement with experiment, but previously non-detected transitions have been found.
Study of the benzene⋅N2 intermolecular potential-energy surface
2003
The intermolecular potential-energy surface pertaining to the interaction between benzene and N2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene–N2 van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene–N2 isotopomers. Experimentally, intermolecula…
The CC3 model : An iterative coupled cluster approach including connected triples
1997
An alternative derivation of many-body perturbation theory (MBPT) has been given, where a coupled cluster parametrization is used for the wave function and the method of undetermined Lagrange multipliers is applied to set up a variational coupled cluster energy expression. In this variational formulation, the nth-order amplitudes determine the energy to order 2n+1 and the nth-order multipliers determine the energy to order 2n+2. We have developed an iterative approximate coupled cluster singles, doubles, and triples model CC3, where the triples amplitudes are correct through second order and the singles amplitudes are treated without approximations due to the unique role of singles as appro…
Fast noniterative orbital localization for large molecules
2006
We use Cholesky decomposition of the density matrix in atomic orbital basis to define a new set of occupied molecular orbital coefficients. Analysis of the resulting orbitals ("Cholesky molecular orbitals") demonstrates their localized character inherited from the sparsity of the density matrix. Comparison with the results of traditional iterative localization schemes shows minor differences with respect to a number of suitable measures of locality, particularly the scaling with system size of orbital pair domains used in local correlation methods. The Cholesky procedure for generating orthonormal localized orbitals is noniterative and may be made linear scaling. Although our present implem…
Cholesky decomposition techniques in electronic structure theory
2011
We review recently developed methods to efficiently utilize the Cholesky decomposition technique in electronic structure calculations. The review starts with a brief introduction to the basics of the Cholesky decomposition technique. Subsequently, examples of applications of the technique to ab inito procedures are presented. The technique is demonstrated to be a special type of a resolution-of-identity or density-fitting scheme. This is followed by explicit examples of the Cholesky techniques used in orbital localization, computation of the exchange contribution to the Fock matrix, in MP2, gradient calculations, and so-called method specific Cholesky decomposition. Subsequently, examples o…
Computational and experimental investigation of intermolecular states and forces in the benzene-helium van der Waals complex
2003
A study of the intermolecular potential-energy surface (IPS) and the intermolecular states of the perprotonated and perdeuterated benzene–He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two- to four-body atom–atom terms is obtained. This IPS, and two other Lennard-Jones atom–atom surfaces from the literature, are each employed in dynamically exact (within the rigid-monomer approximation) calculations of J = 0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational trans…
Large-scale calculations of excitation energies in coupled cluster theory: The singlet excited states of benzene
1996
Algorithms for calculating singlet excitation energies in the coupled cluster singles and doubles (CCSD) model are discussed and an implementation of an atomic-integral direct algorithm is presented. Each excitation energy is calculated at a cost comparable to that of the CCSD ground-state energy. Singlet excitation energies are calculated for benzene using up to 432 basis functions. Basis-set effects of the order of 0.2 eV are observed when the basis is increased from augmented polarized valence double-zeta (aug-cc-pVDZ) to augmented polarized valence triple-zeta (aug-cc-pVTZ) quality. The correlation problem is examined by performing calculations in the hierarchy of coupled cluster models…
Variation of polarizability in the [4n+2] annulene series: from [22]- to [66]-annulene.
2008
Using correlated ab initio methods, the polarizability of large [4n + 2]-annulenes is determined, showing that there exists an almost linear relation between the exaltation of magnetic susceptibility (a measure of aromaticity) and an equivalent enlargement of polarizability.
Argon broadening of the 13CO R(0) and R(7) transitions in the fundamental band at temperatures between 80 and 297K: comparison between experiment and…
2003
We present measurements of Ar-broadening parameters for the R(0) and R(7) lines in the fundamental band of13CO at eight temperatures from 80 to 297 K. The broadening parameters are determined by simultaneous least-squares fitting of spectra recorded using a frequency stabilized diode laser spectrometer. The comparison of the broadening parameter values for R(7) derived at room temperature and different pressures from different line profiles shows that an empirical line profile, which takes into account narrowing effects (Dicke narrowing and absorber speed dependence) but neglects any correlation between collisions, is able to describe the observed lines with constant values of the narrowing…
Polarizabilities of small annulenes from Cholesky CC2 linear response theory
2004
Using recently developed algorithms based on Cholesky decomposition of two-electron integrals to compute response properties at the correlated level, the static and dynamic (at 589 nm) polarizabilities of [4n + 2]-annulenes (n = 1, 2, 3, 4) have been calculated. The results show that the perpendicular component increases along the series linearly with the number of double bonds. The in-plane static polarizability is also increasing linearly with the area of the aromatic ring in the case of the delocalized species. However, linearity is lost for the localized conformations and for the dynamic polarizability. (C) 2004 Elsevier B.V. All rights reserved.
Reduced scaling in electronic structure calculations using Cholesky decompositions
2003
The small numerical rank of the two-electron integral matrix for large molecular systems and large basis sets was demonstrated. Though, the current implementation still requires some improvements on the calculations done in the inner most loop of the decomposition do not exploit the parsity in the Cholesky vectors. With respect to the practical applicability of the presented method an efficient approach to geometrical derivatives was imperative. Such an approach was obtained including certain derivative product functions and decomposing an expanded integral matrix.
Rovibrational structure of the Ar–CO complex based on a novel three-dimensional ab initio potential
2002
The first three-dimensional ab initio intermolecular potential energy surface of the Ar–CO van der Waals complex is calculated using the coupled cluster singles and doubles including connected triples model and the augmented correlation-consistent polarized valence quadruple zeta (aug-cc-pVQZ) basis set extended with a (3s3p2d1f1g) set of midbond functions. The three-dimensional surface is averaged over the three lowest vibrational states of CO. Rovibrational energies are calculated up to 50 cm−1 above the ground state, thus enabling comprehensive comparison between theory and available experimental data as well as providing detailed guidance for future spectroscopic investigations of highe…
Accurate ab initio density fitting for multiconfigurational self-consistent field methods
2008
Using Cholesky decomposition and density fitting to approximate the electron repulsion integrals, an implementation of the complete active space self-consistent field (CASSCF) method suitable for large-scale applications is presented. Sample calculations on benzene, diaquo-tetra- μ -acetato-dicopper(II), and diuraniumendofullerene demonstrate that the Cholesky and density fitting approximations allow larger basis sets and larger systems to be treated at the CASSCF level of theory with controllable accuracy. While strict error control is an inherent property of the Cholesky approximation, errors arising from the density fitting approach are managed by using a recently proposed class of auxi…
Multi-level coupled cluster theory
2014
We present a general formalism where different levels of coupled cluster theory can be applied to different parts of the molecular system. The system is partitioned into subsystems by Cholesky decomposition of the one-electron Hartree-Fock density matrix. In this way the system can be divided across chemical bonds without discontinuities arising. The coupled cluster wave function is defined in terms of cluster operators for each part and these are determined from a set of coupled equations. The total wave function fulfills the Pauli-principle across all borders and levels of electron correlation. We develop the associated response theory for this multi-level coupled cluster theory and prese…
The integral‐direct coupled cluster singles and doubles model
1996
An efficient and highly vectorized implementation of the coupled cluster singles and doubles (CCSD) model using a direct atomic integral technique is presented. The minimal number of n6processes has been implemented for the most time consuming terms and point group symmetry is used to further reduce operation counts and memory requirements. The significantly increased application range of the CCSD method is illustrated with sample calculations on several systems with more than 500 basis functions. Furthermore, we present the basic trends of an open ended algorithm and discuss the use of integral prescreening. © 1996 American Institute of Physics.
The extended CC2 model ECC2
2013
We present a size-extensive extension to the CC2 model that avoids the complications with quasi-degeneracies that are present in the CC2 model and related perturbation theory-based approaches. The formulation also provides a consistent model for treating different parts of a molecular system at different levels of electron correlation. Such a subsystem approach leads to large reductions in the computational requirements without compromising the accuracy. In this initial study, we focus on static molecular properties. © 2013 Copyright Taylor and Francis Group, LLC.
Theoretical absorption spectrum of the Ar–CO van der Waals complex
2003
The three-dimensional intermolecular electric dipole moment surface of Ar–CO is calculated at the coupled cluster singles and doubles level of theory with the aug-cc-pVTZ basis set extended with a 3s3p2d1f1g set of midbond functions. Using the rovibrational energies and wave functions of our recent study [J. Chem. Phys. 117, 6562 (2002)], temperature-dependent spectral intensities are evaluated and compared to available experimental data. Based on the theoretical spectrum, alternative assignments of the experimentally observed lines in the fundamental band of CO around 2160 and 2166 cm−1 are suggested. Thomas.Bondo@uv.es
Coupled cluster calculations of the vertical excitation energies of tetracyanoethylene
2003
The vertical spectrum of tetracyanoethylene was studied using coupled cluster theory. It was found that the lowest singlet-singlet transition, which corresponds to the excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) excitation, occurs at 5.16 eV in the gas phase and is lowered approximately 0.1 eV due to solvent effects in acetonitrile. A parallel study on the ethene spectrum showed the quality of the basis sets and methods used, by placing the V state 7.92 eV above the ground state and giving an energy for the 0-0 transition of 5.42 eV to be compared with the experimental value of 5.50 eV.
Coupled cluster calculations of interaction energies in benzene–fluorobenzene van der Waals complexes
2007
Benzene-fluorobenzene complexes are used as model systems to simulate the interactions of the SBB-HCAII protein-ligand complex. Using the second-order Moller-Plesset [MP2] and the coupled cluster singles and doubles including connected triple excitations models recently implemented with Cholesky decompositions we evaluate accurate interaction energies for several benzene-fluorobenzene van der Waals complexes. We consider edge-to-face interactions and compare the results to those from a recent MP2 study and to experimental findings. In contrast to experimental trends, we find that the interaction tends to decrease with increasing fluorination and conclude that benzene-fluorobenzene complexes…