Gerald Geudtner

MSINDO parameterization for third‐row transition metals

The recently developed MSINDO version of the semiempirical SCF MO method SINDO1 has been parameterized for third‐row transition metals Sc to Zn. The set of reference data used for the previous parameterization of SINDO1 has been substantially increased by incorporating results of recent experiments and first‐principles calculations. A comparison of calculated heats of formation, geometries, ionization potentials, and dipole moments with literature values for more than 200 gas phase molecules is presented. The accuracy of the modified MSINDO version achieved for heats of formation and bond lengths has been considerably improved compared to SINDO1. Small clusters of transition metals and metal oxides were included in the parameterization to ensure accurate results for studies of larger systems. The application of the method to small transition metal complexes that were not included in the parameterization shows that the optimized parameters are transferable to other compounds.

Development of the cyclic cluster approach for ionic systems

The cyclic cluster approach has been implemented in the semiempirical SCF MO method MSINDO for calculations of two‐ and three‐dimensional periodic systems. Several new features are introduced. Special emphasis was given to the description of ionic compounds including long‐range Coulomb interactions. At variance with previous implementations all interaction integrals are calculated in real space. This allows for a direct comparison of results from the cyclic cluster approach and from free and embedded cluster calculations with the original MSINDO method. A scheme based on diatomic contributions was used to calculate analytical gradients for the optimization of lattice parameters. A comparison with extrapolated cluster results for bulk and surface properties of MgO and NiO reveals that relatively small cyclic clusters are sufficient to reach the infinite limit.

Binding energies and bond distances of ion crystal clusters

Abstract Binding energies and bond distances are calculated with the semiempirical MO method SINDO1. A quasilinear relationship is found between normalized binding energies or average bond distances and relative average coordination numbers. It is demonstrated that binding energy per unit and binding energy per bond are not independent and that convergence of both kinds of binding energy to the same bulk value is guaranteed only if their relation is observed.

Theoretical investigations on adsorption at ion crystal surfaces

Abstract Experimental and theoretical methods for the study of adsorption at ion crystal surfaces are reviewed. New Sindo 1 calculations on surface—adsorbate systems are presented in this framework. The special surface systems NaCl, MgO and TiO2 are selected to demonstrate the feasibility of current molecular orbital methods for the generation of surfaces and the study of adsorption of small molecules exemplified by CO2 and H2O. Molecular and dissociative adsorption can be distinguished in the case of adsorbed H2O. A scheme is presented for the systematic improvement of the results. Trends are discussed for geometry, binding characteristics, energetics and infrared spectra of adsorbed molecules. The calculated properties are compared with experimental data.

Treatment of hydrogen bonding in SINDO1

For the treatment of hydrogen bonding in SINDO1, 2p orbitals are introduced on hydrogen. The optimization of the orbital exponent together with the generation of approximate formulas for the core attraction integrals is sufficient to obtain good geometries and binding energies in hydrogen bonded systems. The method is applied to the dimers (H2O)2, (NH3)2, (HF)2, (HCOOH)2, (HCN)2, (H2S)2, and (HCI)2, mixed dimers NH3 · H2O and H2O · HCN, and cyclic polymers (HF)n(n = 3, 4, 6).

Parallelization of the deMon2k code

The parallelization of the LCGTO‐KS‐DFT code deMon2k is presented. The parallelization of the three‐center electron repulsion integrals, the numerical integration using a direct grid algorithm and the matrix multiplication and diagonalization are described. The efficiency of the parallelization is analyzed by selected benchmark calculations. It is shown that geometry optimizations of systems with more than 8000 basis functions are feasible on cluster architectures.

How important are temperature effects for cluster polarizabilities

State-of-the-art first-principle all-electron density functional theory calculations on small sodium clusters are performed to study the temperature dependency of their polarizabilities. For this purpose Born-Oppenheimer molecular dynamics simulations with more than 100,000 time steps (>200 ps) are recorded employing gradient corrected functionals in combination with a double-zeta valence polarization basis set. For each cluster 18 trajectories between 50 and 900 K are collected. The cluster polarizabilities are then calculated along these trajectories employing a triple-zeta valence polarization basis set augmented with field-induced polarization functions. The analysis of these calculations shows that the temperature dependency of the sodium cluster polarizabilities varies strongly with cluster size. For several clusters characteristic changes in the polarizability per atom as a function of temperature are observed. It is shown that the inclusion of finite temperature effects resolves the long-standing mismatch between calculated and measured sodium cluster polarizabilities.

First-Principle Calculations of Large Fullerenes

State of-the-art density functional theory calculations have been performed for the large fullerenes C180, C240, C320, and C540 using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. For the calculations all-electron basis sets were employed. All fullerene structures were fully optimized without symmetry constrains. The analysis of the obtained structures as well as a study on the evolution of the bond lengths and calculated binding energies are presented. The fullerene results are compared to diamond and graphene which were calculated at the same level of theory. This represents the first systematic study on these large fullerenes based on nonsymmetry adapted first-principle calculations, and it demonstrates the capability of DFT calculations for energy and structure computations of large scale structures without any symmetry constraint.

MSINDO parameterization for third-row main group elements

A new parameterization of the SINDO model is introduced in the recently developed MSINDO version for third‐row main group elements Ga, Ge, As, Se, and Br. It is shown that the accuracy achieved for structure and stability as well as ionization potential and dipole moment of compounds containing these elements is good enough to make the extension a suitable tool for the study of larger systems.

Embedding procedure for cluster calculations of ionic crystals

An embedding procedure suitable for Hartree–Fock studies of ionic systems is presented and implemented on the semiempirical level. In this approach model clusters are embedded in finite fields of pseudoatoms with average self‐consistent orbital occupation numbers or fixed orbital occupation numbers for best charge equilibration of cluster atoms. These pseudoatoms are of the same kind and described with the same set of parameters as the real cluster atoms. The implementation in the semiempirical self‐consistent field molecular orbital method SINDO1 is described. Calculations are performed for the systems TiO2 and MgO and the influence of the embedding on geometry and electronic structure is discussed.