We present a simple and efficient embedding scheme for the wave-function based calculation of the energies of local excitations in large systems. By introducing an embedding potential obtained from density-functional theory (DFT) it is possible to describe the effect of an environment on local excitations of an embedded system in wave-function theory (WFT) calculations of the excitation energies. We outline the implementation of such a WFT-in-DFT embedding procedure employing the ADF, Dalton and DIRAC codes, where the embedded subsystem is treated with coupled cluster methods. We then evaluate this procedure in the calculation of the solvatochromic shift of acetone in water and of the f-f spectrum of NpO22+ embedded in a Cs2UO2Cl4 crystal and find that our scheme does effectively incorporate the environment effect in both cases. A particularly interesting finding is that with our embedding scheme we can model the equatorial Cl- ligands in NpO2Cl42- quite accurately, compared to a fully wavefunction-based calculation, and this opens up the possibility of modeling the interaction of different ligands to actinyl species with relatively high accuracy but at a much reduced computational cost.

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The performance of the time-dependent density functional theory (TDDFT) approach has been evaluated for the electronic spectrum of the UO(2)(2+), NUO(+) and NUN molecules. Different exchange-correlation functionals (LDA, PBE, BLYP, B3LYP, PBE0, M06, M06-L, M06-2X, CAM-B3LYP) and the SAOP model potential have been investigated, as has the relative importance of the adiabatic local density approximation (ALDA) to the exchange-correlation kernel. The vertical excitation energies have been compared with reference data obtained using accurate wave-function theory (WFT) methods.

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In this article, we present a consistent derivation of a density functional theory (DFT) based embedding method which encompasses wave-function theory-in-DFT (WFT-in-DFT) and the DFT-based subsystem formulation of response theory (DFT-in-DFT) by Neugebauer [J. Neugebauer, J. Chem. Phys. 131, 084104 (2009)] as special cases. This formulation, which is based on the time-averaged quasi-energy formalism, makes use of the variation Lagrangian techniques to allow the use of nonvariational (in particular: coupled cluster) wave-function-based methods. We show how, in the timeindependent limit, we naturally obtain expressions for the ground-state DFT-in-DFT and WFT-in-DFT embedding via a local potential. We furthermore provide working equations for the special case in which coupled cluster theory is used to obtain the density and excitation energies of the active subsystem. A sample application is given to demonstrate the method.

Relativistic basis sets of double-zeta, triplezeta, and quadruple-zeta quality have been optimized for the lanthanide elements La-Lu. The basis sets include SCF exponents for the occupied spinors and for the 6p shell, exponents of correlating functions for the valence shells (4f, 5d and 6s) and the outer core shells (4d, 5s and 5p), and diffuse functions, including functions for dipole polarization of the 4f shell. A finite nuclear size was used in all optimizations. The basis sets are illustrated by calculations on YbF. Prescriptions are given for constructing contracted basis sets. The basis sets are available as an internet archive and from the Dirac program web site, http://dirac.chem.sdu.dk.The increasing use of all-electron four-component methodology for relativistic effects in molecular structure calculations brings with it a need for high-quality basis sets. Several other authors have generated basis sets at the SCF level for part or all of the periodic table, either with the Dirac Hamiltonian or with the Douglas-Kroll-Hess Hamiltonian [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. While some of these basis sets include correlating functions, a number of them lack the functions needed for valence and outer core correlation and polarization of the SCF sets. In a series of papers [20][21][22][23][24][25][26][27], Dyall has focused on providing consistent basis sets of doublezeta (dz), triple-zeta (tz), and quadruple-zeta (qz) quality for the heavy elements, including correlating functions for the valence and outer core orbitals in the style of the correlation consistent basis sets [28][29][30][31]. So far these basis sets have covered the 4s, 5s, 6s, and 7s blocks; the 4p, 5p, and 6p blocks; the 4d and 5d transition series; and the actinides. This paper continues the series by presenting basis sets for the lanthanides. Work is in progress on the 3d and 6d transition series and the 7p block.The lanthanides have similar challenges to the actinides, but also have some unique features, as far as basis sets are concerned. As for the actinides, the 5d orbital is occupied for several members of the series (La, Ce, Gd, and Lu), and is low-lying for many of the early members of the series. It is in fact doubly occupied in some excited states early in the series. It must therefore be included in the basis set Electronic supplementary material The online version of this article (doi:10.1007/s00214-009-0725-7) contains supplementary material, which is available to authorized users.

Abstract:Applications of quantum chemistry have evolved from single or a few calculations to more complicated workflows, in which a series of interrelated computational tasks is performed. In particular multiscale simulations, which combine different levels of accuracy, typically require a large number of individual calculations that depend on each other. Consequently, there is a need to automate such workflows. For this purpose we have developed PyAdf, a scripting framework for quantum chemistry. PyAdf handles all steps necessary in a typical workflow in quantum chemistry and is easily extensible due to its object-oriented implementation in the Python programming language. We give an overview of the capabilities of PyAdf and illustrate its usefulness in quantum-chemical multiscale simulations with a number of examples taken from recent applications.

In this paper we explore the use of the novel relativistic intermediate Hamiltonian Fock-space coupled-cluster method in the calculation of the electronic spectrum for small actinyl ions ͑NpO 2 + , NpO 2 2+ , and PuO 2 2+ ͒. It is established that the method, in combination with uncontracted double-zeta quality basis sets, yields excitation energies in good agreement with experimental values, and better than those obtained previously with other theoretical methods. We propose the reassignment of some of the peaks that were observed experimentally, and confirm other assignments.