High harmonic spectra computed using time-dependent Kohn-Sham theory with Gaussian orbitals and a complex absorbing potential

High harmonic spectra for H2 are simulated by solving the time-dependent Kohn-Sham equation in the presence of a strong laser field, using an atom-centered Gaussian representation of the orbitals and a complex absorbing potential to mitigate artifacts associated with the finite extent of the basis functions, such as spurious reflection of the outgoing electronic wave packet. Interference between the outgoing and reflected waves manifests in the Fourier transform of the time-dependent dipole moment function and leads to peak broadening in the high harmonic spectrum as well as the appearance of spurious peaks at energies well above the cutoff energy at which the harmonic progression is expected terminate. We demonstrate that well-resolved spectra can be obtained through the use of an atom-centered absorbing potential. As compared to grid-based algorithms for solving the time-dependent Kohn-Sham equations, the present approach is more readily extendible to larger polyatomic molecules.

Study of Electron and Positron Elastic Scattering from Hydrogen Sulphide Using Analytically Obtained Static Potential

A detailed study of elastic scattering of electrons and positrons from a hydrogen sulphide (H2S) molecule is presented using the method of partial wave phase shift analysis with suitably chosen complex optical potentials. The important aspect of our present work is that we uniquely obtain static potential in an analytical form and use it along with exchange (only for electron), polarization and purely imaginary absorption potentials to define the complex optical potential. The static potential is evaluated by obtaining charge density from the H2S molecule using the molecular wavefunction represented through an accurate analytical form of the Gaussian orbitals. The primary aim of our study is to test our present approach, as applied to the electron and positron scattering from H2S. Therefore, the results for electron and positron impact differential, integral, momentum-transfer, absorption and total cross sections are obtained for the incident energies in the range of 10–500 eV. Comparisons of these different types of cross section results with the available measurements and other calculations show good agreement, which suggests the applicability of our present approach.

Mathematical Analysis of a Series of 4-Acetylamino-2-(3,5-dimethylpyrazol-1-yl)-6-pyridylpyrimidines: A Simple Way to Relate Quantum Similarity to Local Chemical Reactivity Using the Gaussian Orbitals Localized Theory

Molecular Quantum Similarity (MQS) descriptors and Density Functional Theory (DFT) based reactivity descriptors were studied for a series of 4-Acetylamino-2-(3,5-dimethylpyrazol-1-yl)-6-pyridylpyrimidines compounds used for Parkinson’s disease (PD) treatment. The quantification of the steric and electronic effects was shown through scales of quantitative convergence; such scales allow us to establish a methodology to quantify the similarity from the local chemical reactivity (Fukui Functions) point of view. This procedure provides new considerations in the local reactivity of the A2A Adenosine receptor antagonists in a disease of difficult control as PD. In addition, we present new considerations to the localized bonding theory and show a new methodology for quantum similarity on the Fukui Functions. Considering that the Fukui functions under a condensation scheme may have ambiguities in the (DFT) context.

Compton Profiles and Nature of Bonding in Tantalum Chalcogenides

We report the Compton profiles of tantalum chalcogenides (TaS2 and TaSSe) using Hartree–Fock and hybridization of Hartree–Fock and density functional theories within linear combination of atomic (Gaussian) orbitals. To interpret the theoretical data on Compton line shapes, we have measured the Compton profiles using our in-house 100 mCi 241Am γ-ray Compton spectrometer. To understand the relative nature of bonding, we have obtained the equal-valence-electron-density (EVED) profiles. The EVED profiles shows that charge in TaSSe is more localized than TaS2 in the bonding direction which confirms that TaSSe is more covalent than TaS2, which is in agreement with the Mulliken’s population analysis.