Hans Peter Lüthi

INTERACTION ENERGIES OF VAN DER WAALS AND HYDROGEN BONDED SYSTEMS CALCULATED USING DENSITY FUNCTIONAL THEORY: ASSESSING THE PW91 MODEL

The performance of density functional theory using the Perdew and Wang’s exchange and correlation functionals (PW91) functional for the prediction of intermolecular interactionenergies is evaluated based on calculations on the neon, argon, methane, ethylene, and benzene dimers, as well as on 12 hydrogen bonded complexes (water, methanol, formic acid, hydrogen fluoride, ammonia, formamide dimers and water–methanol, water–dimethyl ether, water–formaldehyde, hydrogen cyanide–hydrogen fluoride, water–ammonia, water–formamide complexes). The results were compared with those obtained from Becke’s exchange and Lee, Yang, and Parr’s correlation functionals (BLYP), Becke’s 3 parameter functional combined with Lee, Yang, and Parr’s correlation functional (B3LYP), second order Mo/ller–Plesset perturbation (MP2), and coupled cluster calculations with single and double substitutions and with non-iterative triple corrections [CCSD(T)] calculations. The calculated interactionenergies show that the PW91 functional performs much better than the BLYP or B3LYP functionals. The error in the computed binding energies of the hydrogen bonded complexes is 20% in the worst case. The most demanding cases are the systems with large dispersion contributions to the binding energy, such as the benzene dimer. In contrast to the BLYP and B3LYP functionals which fail to account for dispersion, the PW91 functional at least partly recovers the attraction. The basis set dependence of the PW91 functionals is relatively small in contrast to the MP2 and CCSD(T) methods. Despite its occasional difficulties with dispersion interaction, the PW91 functional may be a viable alternative to the ab initio methods, certainly in situations where large complexes are being studied.

On the accurate calculation of polarizabilities and second hyperpolarizabilities of polyacetylene oligomer chains using the CAM-B3LYP density functional

The polarizability and second hyperpolarizability of polyacetylene oligomer chains of increasing size up to C(24)H(26) were investigated by means of the Coulomb-attenuating method (CAM-B3LYP) using response theory. It was found that this long-range corrected density functional removes to large parts the overestimation observed for standard methods and in many cases provides results close to those of coupled cluster calculations. A direct comparison to experimentally observed dynamic hyperpolarizabilities is made to estimate the accuracy of the method. A basis set study revealed a noticeable contribution of diffuse orbitals to the hyperpolarizability also for larger oligomers. Furthermore, CAM-B3LYP is also confirmed to provide molecular geometries close to experimentally observed structures, especially for longer chain lengths.

Binding energies, molecular structures, and vibrational frequencies of transition metal carbonyls using density functional theory with gradient corrections

The performance of the density functional theory (DFT) methods with different gradient corrections as an approach for the computation of transition metal complexes has been evaluated. As a test, the structures, binding energies, and vibrational frequencies of a series of binary transition metal carbonyl complexes were calculated. Comparison with previous studies shows that the gradient correction significantly improves the performance of the DFT schemes, and that the results obtained generally match the quality of the data obtained from coupled cluster and pair functional methods.

AN AB INITIO DERIVED TORSIONAL POTENTIAL ENERGY SURFACE FOR (H2O)3. II: BENCHMARK STUDIES AND INTERACTION ENERGIES

A torsional potential energy surface for the cyclic water trimer was calculated at the level of second‐order Mo/ller–Plesset perturbation theory. For the construction of this ab initio surface, the first‐order wave function was expanded in a many‐electron basis which linearly depends on the interelectronic coordinates r12. The one‐electron basis of Gaussian orbitals was calibrated on the water monomer and dimer to ensure that the ab initio surface computed represents the (near‐ ) basis set limit for the level of theory applied. The positions of the free O—H bonds are described by three torsional angles. The respective three‐dimensional torsional space was investigated by 70 counterpoise corrected single‐point calculations for various values of these angles, providing a grid to fit an analytical representation of the potential energy surface. The four symmetry unique stationary points previously found at the Hartree–Fock and conventional Mo/ller–Plesset levels [Schutz et al., J. Chem. Phys. 99, 5228 (1993)...

How well does the Hartree–Fock model predict equilibrium geometries of transition metal complexes? Large‐scale LCAO–SCF studies on ferrocene and decamethylferrocene

Large scale ab initio LCAO–SCF calculations performed on ferrocene show that the Hartree–Fock model is unable to account for the experimentally observed metal to ring distance. The present results, using basis sets of better than triple zeta quality, show that both the equilibrium geometry and the orbital energies have converged already at the double zeta level (metal‐ring distance;1.89 A, i.e., 15% larger than the experimental value of 1.65 A). A comparative calculation on decamethylferrocene yields essentially the same results. These findings raise some doubts as to the adequacy of the Hartree–Fock model for predictions of equilibrium geometries of transition metal complexes in general.

Electronic structure optimization in plane-wave-based density functional calculations by direct inversion in the iterative subspace

Abstract We adopted the method of direct inversion in the iterative subspace (DIIS) to plane-wave-based electronic structure calculations. We show that with simple modifications based on the idea of preconditioning, the DIIS method is very efficient and robust. A discussion of the merits of the new method relative to other approaches is also given.

Ab initio computations close to the one‐particle basis set limit on the weakly bound van der Waals complexes benzene–neon and benzene–argon

The equilibrium geometries and binding energies of the van der Waals (vdW) complexes benzene–neon and benzene–argon have been calculated at the level of second‐order Mo/ller–Plesset perturbation theory (MP2). Terms linear in the interelectronic distances r12 were used in the MP2 treatment to converge fast to the one‐particle basis set limit. This new method, MP2‐R12 as implemented in the sore program, was applied with high quality basis sets derived from Dunning’s aug‐cc‐pVXZ (X=D,T,Q,5) sets. In reward of the efforts to reach the basis set limit, it is found that the calculated binding energies for the vdW complexes were computed virtually free of a basis set superposition error (BSSE). The key MP2‐R12 results are De=154 cm−1 and re=3.32 A for benzene–neon and De=553 cm−1 and re=3.41 A for benzene–argon. The permanent dipole moments of the vdW complexes have been computed by finite field perturbation theory. Coupled‐cluster calculations of type CCSD(T), although performed with considerably smaller basis ...

The MP2 limit correction applied to coupled cluster calculations of the electronic dissociation energies of the hydrogen fluoride and water dimers

The basis set convergence of ab initio computed electronic dissociation energies is reported for the hydrogen bonded complexes (HF)2 (H2O)2. At the level of CCSD(T) theory (coupled cluster model with singles, doubles, and approximate connected triples), the interaction energy is split into one- and two-body terms, and corrections such as the counterpoise (CP) and the MP2 limit are explored. The MP2-limit correction consists of substituting the second-order Moller-Plesset (MP2) perturbation theory contribution computed with the actual basis set by the limiting value that is obtained in a complete basis. Clearly the basis set convergence of the CCSD(T) calculations is improved by the MP2 limit correction. Moreover, the MP2-limit correction can be applied irrespective of whether or not the two-body term has been CP corrected beforehand. Little difference is found between the two possibilities, but the most accurate results are obtained by applying the MP2 limit correction to CP corrected CCSD(T) two-body ter...

Time-dependent density-functional theory investigation of the formation of the charge transfer excited state for a series of aromatic donor–acceptor systems. Part II

Singlet excitation energies for a series of acceptor para-substituted N,N-dimethyl-anilines that are dual (4DMAB-CN, 3M4MAB-CN, MHD) and nondual (4AB-CN, 3M4AB-CN, 4MAB-CN, 3M4DMAB-CN, HHD, and MMD) fluorescent have been performed using the TDDFT method. The aim of this study is to investigate the influence of changing donor groups as well as the addition of methyl groups to the benzene moiety, on the fluorescence behavior of these molecules. Calculations of excitation energies have been performed with both B3LYP and MPW1PW91 functionals using a 6-311*(2p,d) (Bg) basis set. For all systems, ground-state geometries were optimized using density-functional theory with the Becke three parameter Lee–Yang–Parr functional combined with a 6-31G(d) (Sm) basis set. In addition, 4AB-CN, 4DMAB-CN, and MMD ground-state geometry has also been optimized using the MPW1PW91 functional with the Sm basis set. For all molecules, the potential energy surface (PES) has been investigated following the twisting intramolecular ch...

Towards the accurate computation of properties of transition metal compounds: the binding energy of ferrocene

Abstract Recently published ab initio computations on ferrocene in the framework of coupled-cluster as well as multireference perturbation theory are exploited to obtain a theoretical best estimate of 655 ± 15 kcal/mol for the heterolytic bond disruption enthalpy. This best estimate was obtained by establishing the complete atomic orbitals basis set limit at the level of single-reference second-order perturbation theory, and computing corrections for relativistic effects, semicore (3s/3p) electron correlation effects, vibrational zero-point energy corrections, and structural relaxation energies of the fragments. Agreement with the experimental value of 635 ± 6 kcal/mol is unsatisfactory.