Henryk A. Witek

Learn More
Recently developed parameters for five first-row transition-metal elements (M = Sc, Ti, Fe, Co, and Ni) in combination with H, C, N, and O as well as the same metal (M-M) for the spin-polarized self-consistent-charge density-functional tight-binding (DFTB) method have been calibrated. To test their performance a couple sets of compounds have been selected(More)
The Criegee intermediates are carbonyl oxides postulated to play key roles in the reactions of ozone with unsaturated hydrocarbons; these reactions constitute an important mechanism for the removal of unsaturated hydrocarbons and for the production of OH in the atmosphere. Here, we report the transient infrared (IR) absorption spectrum of the simplest(More)
In this work, we derive and test a new automatized strategy to construct repulsive potentials for the self-consistent charge density functional tight-binding (SCC-DFTB) method. This approach allows one to explore the parameter space in a systematic fashion in order to find optimal solutions. We find that due to the limited flexibility of the SCC-DFTB(More)
A parametrization scheme for the electronic part of the density-functional based tight-binding (DFTB) method that covers the periodic table is presented. A semiautomatic parametrization scheme has been developed that uses Kohn-Sham energies and band structure curvatures of real and fictitious homoatomic crystal structures as reference data. A confinement(More)
Ammonia adsorption on single-walled carbon nanotubes (SWNTs) was studied by means of infrared spectroscopy at both cryogenic (approximately 94 K) and room (approximately 300 K) temperatures. At 94 K, vacuum-annealed SWNTs showed no detectable ammonia uptake. However, the ammonia adsorption was found to be sensitive to the functionalities and defects on the(More)
Closed-form, general formulas for the Zhang-Zhang (ZZ) polynomials for two important classes of benzenoid structures, chevrons ‫݄ܥ‬ሺ݇ǡ ݉ǡ ݊ሻ and generalized chevrons ‫݄ܥ‬ሺ݇ǡ ݉ǡ ݊ ଵ ǡ ݊ ଶ ሻ, are formally derived. The derivations rely on a new and important theorem, which states that the ZZ polynomial of two fused parallelograms can be represented as the(More)
We employ the self-consistent-charge density-functional tight-binding (SCC-DFTB) method for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all 35 five- and six-member rings containing isomers of small fullerenes, C20, C24, C26, C28, C30, C32, C34, and C36, as first part of a(More)
We employ a graphical proof-oriented tool, ZZDecomposer, to discover formal derivations of Zhang-Zhang (ZZ) polynomials for various families and subfamilies of benzenoid structures including tripods, zigzag-edge coronoids fused with a starphene, oblate rectangles ܱ‫ݎ‬ሺ݉ǡ ʹሻ, decompositions of the analyzed structures. The decompositions provide appropriate(More)