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- Garcia Cuesta, Inmaculada, et al.
(författare)
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Variation of polarizability in the [4n+2] annulene series: from [22]- to [66]-annulene
- 2008
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 10:3, s. 361-365
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Aidas, Kestutis, et al.
(författare)
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The Dalton quantum chemistry program system
- 2014
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Ingår i: Wiley Interdisciplinary Reviews. Computational Molecular Science. - : Wiley. - 1759-0876. ; 4:3, s. 269-284
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Tidskriftsartikel (refereegranskat)abstract
- 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, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.
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| 6. |
- Aquilante, Francesco, et al.
(författare)
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Accurate ab initio density fitting for multiconfigurational self-consistent field methods
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:2, s. 024113-
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Tidskriftsartikel (refereegranskat)abstract
- 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-mu-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 auxiliary basis sets constructed from Cholesky decomposition of the atomic electron repulsion integrals.
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| 7. |
- Aquilante, Francesco, et al.
(författare)
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Cholesky decomposition techniques in electronic structure theory
- 2011
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Ingår i: Linear-Scaling Techniques in Computational Chemistry and Physics. - Dordrecht : Springer. - 9789048128525 ; , s. 301-304
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- 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 contributionto the Fock matrix, in MP2, gradient calculations, and so-called method specific Cholesky decomposition. Subsequently, examples of calibration of the method with respect to computed total energies, excitation energies, and auxiliary basis set pruning are presented. In particular, it is demonstrated that the Cholesky method is an unbiased method to derive auxiliary basis sets. Furthermore, details of the implementational considerations are put forward and examples from a parallel Cholesky decomposition scheme is presented. Finally, an outlook and perspectives are presented, followed by a summary and conclusions section. We are of the opinion that the Cholesky decomposition method is a technique that has been overlooked for too long. We have just recently started to understand how to efficiently incorporate the method in existing ab initio programs. The full potential of the Cholesky technique has not yet been fully explored.
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| 8. |
- Aquilante, Francesco, et al.
(författare)
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Fast noniterative orbital localization for large molecules.
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:17
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Tidskriftsartikel (refereegranskat)abstract
- 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 implementation scales cubically, the algorithm is significantly faster than any of the conventional localization schemes. In addition, since this approach does not require starting orbitals, it will be useful in local correlation treatments on top of diagonalization-free Hartree-Fock optimization algorithms.
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| 9. |
- Fernandez, Berta, et al.
(författare)
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Coupled cluster calculations of interaction energies in benzene-fluorobenzene van der Waals complexes
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 441:4-6, s. 332-335
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Tidskriftsartikel (refereegranskat)abstract
- 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 are too simple to simulate the full SBB-HCAII protein-ligand system. (c) 2007 Elsevier B.V. All rights reserved.
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| 10. |
- Lopez Cacheiro, Javier, et al.
(författare)
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The CCSD(T) Model With Cholesky Decomposition of Orbital Energy Denominators
- 2011
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608. ; 111:2, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- 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 implementation shows a speed-up factor larger than O-2/V, where O is the number of occupied and V the number of virtual orbitals, and in general at most 5 vectors are needed to get a precision of mu E-h. We demonstrate that the Cholesky algorithm is better suited for studying large systems. (c) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 349-355, 2011
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