Rika Kobayashi

The Dalton quantum chemistry program system

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, Møller–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 http://www.daltonprogram.org for a number of UNIX platforms.

Assessment of the efficiency of long-range corrected functionals for some properties of large compounds

Using the long-range correction (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated a series of properties that are known to be poorly reproduced by standard functionals: Bond length alternation of pi-conjugated polymers, polarizabilities of delocalized chains, and electronic spectra of extended dyes. For each of these properties, we present cases in which traditional hybrid functionals do provide accurate results and cases in which they fail to reproduce the correct trends. The quality of the results is assessed with regard to experimental values and/or data arising from electron-correlated wave function approaches. It turns out that (i) both LC-DFT and CAM-B3LYP provide an accurate bond length alternation for polyacetylene and polymethineimine, although for the latter they decrease slightly too rapidly with chain length. (ii) The LC generalized gradient approximation and MP2 polarizabilities of long polyphosphazene and polymethineimine oligomers agree almost perfectly. In the same way, CAM-B3LYP corrects the major part of the B3LYP faults. (iii) LC and CAM techniques do not help in correcting the nonrealistic evolution with chain length of the absorption wavelengths of cyanine derivatives. In addition, though both schemes significantly overestimate the ground to excited state transition energy of substituted anthraquinone dyes, they provide a more consistent picture once a statistical treatment is performed than do traditional hybrid functionals.

Multiconfigurational self‐consistent field calculations of nuclear shieldings using London atomic orbitals

Nuclear shielding calculations are presented for multiconfigurational self‐consistent field wave functions using London atomic orbitals (gauge invariant atomic orbitals). Calculations of nuclear shieldings for eight molecules (H2O, H2S, CH4, N2, CO, HF, F2, and SO2) are presented and compared to corresponding individual gauges for localized orbitals (IGLO) results. The London results show better basis set convergence than IGLO, especially for heavier atoms. It is shown that the choice of active space is crucial for determination of accurate nuclear shielding constants.

CALCULATION OF SIZE-INTENSIVE TRANSITION MOMENTS FROM THE COUPLED CLUSTER SINGLES AND DOUBLES LINEAR RESPONSE FUNCTION

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 C4 and 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 the 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 negative dipole strength for the lowest totally symmetric dipole allowed transition for 19 or more noninteracting LiH systems. The CCLR approach is shown to be a very attractive ‘‘black box’’ approach for the calculation of transition moments.

First hyperpolarizability of polymethineimine with long-range corrected functionals

Using the long-range corrected (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated the longitudinal dipole moments and static electronic first hyperpolarizabilities of increasingly long polymehtineimine oligomers. For comparison purposes Hartree-Fock (HF), Moller-Plesset perturbation theory (MP2), and conventional pure and hybrid functionals have been considered as well. HF, generalized gradient approximation (GGA), and conventional hybrids provide too large dipole moments for long oligomers, while LC-DFT allows to reduce the discrepancy with respect to MP2 by a factor of 3. For the first hyperpolarizability, the incorrect evolution with the chain length predicted by HF is strongly worsened by BLYP, Perdew-Burke-Ernzerhof (PBE), and also by B3LYP and PBE0. On the reverse, LC-BLYP and LC-PBE hyperpolarizabilities are correctly predicted to be positive (but for the two smallest chains). Indeed, for medium and long oligomers LC hyperpolarizabilities are slightly smaller than MP2 hyperpolarizabilities, as it should be. CAM-B3LYP also strongly improves the B3LYP results, though a bit less impressively for small chain lengths. The present study demonstrates the efficiency of long-range DFT, even in very pathological cases.

A direct atomic orbital driven implementation of the coupled cluster singles and doubles (CCSD) model

The coupled cluster singles and doubles (CCSD) model has been implemented using a direct atomic integral driven technique. The atomic integrals are generated in distributions with one fixed and three free indices, and one distribution is stored in fast memory together with the cluster amplitudes and the cluster vector function. Little loss in efficiency has been obtained compared to a molecular orbital integral driven technique. Sample calculations are presented for HFCO containing 328 basis functions.

Calculation of frequency-dependent polarizabilities using coupled-cluster response theory

Abstract Coupled-cluster singles and doubles linear response (CCLR) calculations have been presented for frequency-dependent dipole polarizabilities and the results compared with the results from a CI-like approach to the equation of motion (EOMCC). The frequency-dependent polarizabilities are similar in the two approaches for single molecule calculations on small systems. However, the CCLR approach gives size-extensive polarizabilities, whereas the EOMCC approach does not. EOMCC calculations can therefore give unphysical polarizabilities, e.g. EOMCC calculations on a sequence of non-interacting LiH systems gave a negative polarizability for 20 or more non-interacting LiH systems. The CCLR approach is shown to be an attractive “black box” approach for the calculation of accurate frequency-dependent polarizabilities.

Gradient theory applied to the Brueckner doubles method

The Brueckner doubles variant of coupled cluster theory has recently been reintroduced by the authors. The use of Brueckner orbitals means that the governing equations for T2 take a particularly simple form. Here we give the details for the evaluation of the gradient of the Brueckner doubles energy for (a) the unrestricted spin–orbital formalism and (b) the closed‐shell restricted formalism. Applications are presented for H2O, NH3, CH4, H2CO, C2H2, HCN, and CO2 and comparisons are made with the Hartree–Fock, second order Mo/ller–Plesset and quadratic configuration interaction models and with experiment.

Studies of the ground and excited-state surfaces of the retinal chromophore using CAM-B3LYP

The isomerization of the 11-cis isomer (PSB11) of the retinal chromophore to its all-trans isomer (PSBT) is examined. Optimized structures on both the ground state and the excited state are calculated, and the dependence on torsional angles in the carbon chain is investigated. Time-dependent density functional theory is used to produce excitation energies and the excited-state surface. To avoid problems with the description of excited states that can arise with standard DFT methods, the CAM-B3LYP functional was used. Comparing CAM-B3LYP with B3LYP results indicates that the former is significantly more accurate, as a consequence of which detailed cross sections of the retinal excited-state surface are obtained.

Comparison of coupled-cluster and Brueckner coupled-cluster calculations of molecular properties

Abstract The dipole moment, polarizabilities and hyperpolarizabilities of Ne, Be, BH, CH+, CO and NNO have been determined using the coupled-cluster and Brueckner coupled-cluster methods. The effect of orbital relaxation on these properties has been investigated implicitly, by carrying out singles and doubled coupled-cluster (CCSD) calculations with and without field relaxed SCF orbitals and explicitly through carrying out Brueckner doubles (BCCD) calculations. The effect of the connected triple excitations has been considered in the methods CCSD(T) and BCCD(T). The results show that allowing the SCF orbitals to relax in the presence of the field can make a significant difference to the CCSD properties. It has also been found that CCSD with field relaxed SCF orbitals and BCCD give similar results.