Vincenzo Tschinke

Bio: Vincenzo Tschinke is an academic researcher from University of Calgary. The author has contributed to research in topics: Bond energy & Hartree–Fock method. The author has an hindex of 11, co-authored 18 publications receiving 1102 citations.

Calculation of bond energies in compounds of heavy elements by a quasi-relativistic approach

Abstract: A quasi-relativistic method, in which the valence density is optimized with respect to the first-order relativistic Hamiltonian, has been evaluated by calculations on systems containing heavy elements including third-row transition metals and actinides. The method adopts the statistical energy expression and employs in addition the frozen core approximation. The quasi-relativistic method has been applied in calculations on atomic orbital energies for the valence shells of heavy elements. It is concluded from these calculations that the quasi-relativistic scheme affords results in better accord with the fully relativistic Dirac-Slater method than the first-order relativistic method based on perturbation theory. Calculations on the M-X bond energies in MX{sub 4} (M = Th, U; X = F, Cl, Br, I) as well as the M-R bond energies in Cl{sub 3}MR (M = Th, U; R = H, CH{sub 3}) revealed in addition that bond energies based on the quasi-relativistic method (QR) were in better agreement with experimental data than bond energies based on the first-order perturbation theory (FO). The absolute mean derivations with respect to experimental values were 6.9 and 16.5 kcal mol{sup {minus}1} for QR and FO, respectively, the case of the MX{sub 4} systems. It is concluded that the quasi-relativistic method, inmore » which changes in the electron density induced by relativity ({Delta}{rho}{sup R}) are approximately taken into account in the energy expression, should be used for compounds containing actinides. Both QR and FO (in which contributions from {Delta}{rho}{sup R} to the total energy are absent, even though they are present in the orbital energies) are appropriate for elements up to Z = 80, although QR represents a slight improvement for the elements in the third transition series.« less

Theoretical-Study on the Electronic and Molecular-Structures of (C5H5)M(L) (M = Rh, Ir, L = CO, PH3) and M(CO)4 (M = Ru, Os) and their Ability to Activate the C-H Bond in Methane

Abstract: Nonlocal density functional calculations have been carried out on the electronic and molecular structures of (C{sub 5}H{sub 5})M(L) (L = CO, PH{sub 3}; M = Rh, Ir) (a) and M(CO){sub 4} (M = Ru, Os) (b). All systems are found to have a singlet ground state. Optimized geometries are reported for each system on the singlet ground state as well as the first excited triplet state. Calculated dissociation energies are presented for Y = CO, PH{sub 3}, and H{sub 2} in the case of X{sub n}M = a and for Y = CO and H{sub 2} in the case of X{sub n}M = b. Complete reaction profiles have been calculated for the oxidative addition of H{sub 2} and CH{sub 4} to a and b. The addition reactions are found to be more facile for a than for b. It is argued that a is unique as a C-H activating agent in having only empty {sigma}-type d-based orbitals interacting with the incoming C-H bond. Calculations are presented on the reaction enthalpies of the H-H and C-H addition processes along with the M-H and M-CH{sub 3} bond energies.

Chemistry with ADF

Abstract: We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order-N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency-dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF-typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation-strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time-dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001

Rationale for mixing exact exchange with density functional approximations

Abstract: Density functional approximations for the exchange‐correlation energy EDFAxc of an electronic system are often improved by admixing some exact exchange Ex: Exc≊EDFAxc+(1/n)(Ex−EDFAx). This procedure is justified when the error in EDFAxc arises from the λ=0 or exchange end of the coupling‐constant integral ∫10 dλ EDFAxc,λ. We argue that the optimum integer n is approximately the lowest order of Gorling–Levy perturbation theory which provides a realistic description of the coupling‐constant dependence Exc,λ in the range 0≤λ≤1, whence n≊4 for atomization energies of typical molecules. We also propose a continuous generalization of n as an index of correlation strength, and a possible mixing of second‐order perturbation theory with the generalized gradient approximation.

Relativistic regular two‐component Hamiltonians

Abstract: In this paper, potential‐dependent transformations are used to transform the four‐component Dirac Hamiltonian to effective two‐component regular Hamiltonians. To zeroth order, the expansions give second order differential equations (just like the Schrodinger equation), which already contain the most important relativistic effects, including spin–orbit coupling. One of the zero order Hamiltonians is identical to the one obtained earlier by Chang, Pelissier, and Durand [Phys. Scr. 34, 394 (1986)]. Self‐consistent all‐electron and frozen‐core calculations are performed as well as first order perturbation calculations for the case of the uranium atom using these Hamiltonians. They give very accurate results, especially for the one‐electron energies and densities of the valence orbitals.

Design of Density Functionals by Combining the Method of Constraint Satisfaction with Parametrization for Thermochemistry, Thermochemical Kinetics, and Noncovalent Interactions.

Abstract: We present a new hybrid meta exchange-correlation functional, called M05-2X, for thermochemistry, thermochemical kinetics, and noncovalent interactions. We also provide a full discussion of the new M05 functional, previously presented in a short communication. The M05 functional was parametrized including both metals and nonmetals, whereas M05-2X is a high-nonlocality functional with double the amount of nonlocal exchange (2X) that is parametrized only for nonmetals. In particular, M05 was parametrized against 35 data values, and M05-2X is parametrized against 34 data values. Both functionals, along with 28 other functionals, have been comparatively assessed against 234 data values: the MGAE109/3 main-group atomization energy database, the IP13/3 ionization potential database, the EA13/3 electron affinity database, the HTBH38/4 database of barrier height for hydrogen-transfer reactions, five noncovalent databases, two databases involving metal−metal and metal−ligand bond energies, a dipole moment databas...

Relativistic total energy using regular approximations

Abstract: In this paper we will discuss relativistic total energies using the zeroth order regular approximation (ZORA). A simple scaling of the ZORA one‐electron Hamiltonian is shown to yield energies for the hydrogenlike atom that are exactly equal to the Dirac energies. The regular approximation is not gauge invariant in each order, but the scaled ZORA energy can be shown to be exactly gauge invariant for hydrogenic ions. It is practically gauge invariant for many‐electron systems and proves superior to the (unscaled) first order regular approximation for atomic ionization energies. The regular approximation, if scaled, can therefore be applied already in zeroth order to molecular bond energies. Scalar relativistic density functional all‐electron and frozen core calculations on diatomics, consisting of copper, silver, and gold and their hydrides are presented. We used exchange‐correlation energy functionals commonly used in nonrelativistic calculations; both in the local‐density approximation (LDA) and including...