Study of Positron Impact Scattering from Methane and Silane Using an Analytically Obtained Static Potential with Correlation Polarization

A detailed study of positron impact elastic scattering from methane and silane is carried out using a model potential consisting of static and polarization potentials. The static potential for the molecular target is obtained analytically by using accurate Gaussian molecular wavefunctions. The molecular orbitals are expressed as a linear combination of Gaussian atomic orbitals. Along with the analytically obtained static potential, a correlation polarization potential is also added to construct the model potential. Utilizing the model potential, the Schrödinger equation is solved using the partial wave phase shift analysis method, and the scattering amplitude is obtained in terms of the phase shifts. Thereafter, the differential, integrated and total cross sections are calculated. These cross-section results are compared with the previously reported measurements and theoretical calculations.

How to Calculate Condensed Matter Electronic Structure Based on Multi-Electron Atom Semi-Classical Model

Atoms are proved to be semi-classical electronic systems in the sense of closeness of their exact quantum electron energy spectrum with that calculated within semi-classical approximation. Introduced semi-classical model of atom represents the wave functions of bounded in atom electrons in form of hydrogen-like atomic orbitals with explicitly defined effective charge numbers. The hydrogen-like electron orbitals of constituting condensed matter atoms are used to calculate the matrix elements of the secular equation determining the condensed matter electronic structure in the linear-combination-of-atomic-orbitals (LCAO) approach. Preliminary test calculations are conducted for boron B atom and diboron B2 molecule electron systems.

Quasi-Relativistic Calculation of EPR g-Tensors with Derivatives of the Decoupling Transformation, Gauge-Including Atomic Orbitals, and Magnetic Balance

We present an exact two-component (X2C) ansatz for the EPR g-tensor using gauge-including atomic orbitals (GIAOs) and a magnetically balanced basis set expansion. In contrast to previous X2C and "fully" relativistic ansätze for the g-tensor, this implementation results in a gauge-origin invariant formalism. Furthermore, the derivatives of the relativistic decoupling matrix are considered to form the complete analytical derivative of the X2C Hamiltonian. To reduce the associated computational costs, we apply the diagonal local approximation to the unitary decoupling transformation (DLU) and the (multipole-accelerated) resolution of the identity approximation. The X2C ansatz is compared to Douglas-Kroll-Hess theory and the zeroth-order regular approximation for 11 diatomic molecules. The impact of the relativistic Hamiltonian, the basis set, and the density functional approximation is subsequently assessed for a set of 17 transition-metal complexes to complement our previous work on the hyperfine coupling constant [DOI: 10.33774/chemrxiv-2021-wnz1v-v2]. In total, 24 basis sets and 22 density functional approximations are considered. The quasi-relativistic X2C and DLU-X2C Hamiltonians accurately reproduce the results of the parent "fully" relativistic four-component theory when accounting for two-electron picture-change effects with the modified screened nuclear spin-orbit approximation in the respective one-electron integrals and integral derivatives. Generally, the uncontracted Dyall and segmented-contracted Karlsruhe x2c-type basis sets perform well when compared to large even-tempered basis sets. Moreover, (range-separated) hybrid density functional approximations are needed to match the experimental findings. Here, hybrids based on the meta -generalized gradient approximation are not an a priori improvement. Compared to the other computational parameters, the impact of the GIAOs and the magnetic balance on the actual results in standard calculations is less pronounced. Routine calculations of large molecules are possible with widely available and comparably low- cost hardware as demonstrated for [Pt(C6Cl5)4]− with 3360 basis functions and three spin-(1/2) La(II) and Lu(II) compounds. Both approaches based on a common gauge origin and GIAOs using triple- ζ basis sets lead to a good agreement with the experimental findings. The best agreement is found with hybrid functionals such as PBE0 and ωB97X-D.

Boosting proximity spin–orbit coupling in graphene/WSe2 heterostructures via hydrostatic pressure

Van der Waals heterostructures composed of multiple few layer crystals allow the engineering of novel materials with predefined properties. As an example, coupling graphene weakly to materials with large spin–orbit coupling (SOC) allows to engineer a sizeable SOC in graphene via proximity effects. The strength of the proximity effect depends on the overlap of the atomic orbitals, therefore, changing the interlayer distance via hydrostatic pressure can be utilized to enhance the interlayer coupling between the layers. In this work, we report measurements on a graphene/WSe2 heterostructure exposed to increasing hydrostatic pressure. A clear transition from weak localization to weak antilocalization is visible as the pressure increases, demonstrating the increase of induced SOC in graphene.

First Principles Calculations of Atomic and Electronic Structure of TiAl3+- and TiAl2+-Doped YAlO3

In this paper, the density functional theory accompanied with linear combination of atomic orbitals (LCAO) method is applied to study the atomic and electronic structure of the Ti3+ and Ti2+ ions substituted for the host Al atom in orthorhombic Pbnm bulk YAlO3 crystals. The disordered crystalline structure of YAlO3 was modelled in a large supercell containing 160 atoms, allowing simulation of a substitutional dopant with a concentration of about 3%. In the case of the Ti2+-doped YAlO3, compensated F-center (oxygen vacancy with two trapped electrons) is inserted close to the Ti to make the unit cell neutral. Changes of the interatomic distances and angles between the chemical bonds in the defect-containing lattices were analyzed and quantified. The positions of various defect levels in the host band gap were determined.

Spin-resolved charge density and wavefunction refinements using MOLLYNX: a review

MOLLYNX is a new crystallographic tool developed to access a more precise description of the spin-dependent electron density of magnetic crystals, taking advantage of the richness of experimental information from high-resolution X-ray diffraction (XRD), unpolarized neutron (UND) and polarized neutron diffraction (PND). This new program is based either on the well known Hansen–Coppens multipolar model (MOLLYNX-mult) or on a new expansion over a set of atomic orbitals (MOLLYNX-orb). The main difference between the two models is the basis of the expansion: in MOLLYNX-mult the expansion is over atom centered real spherical harmonics, in MOLLYNX-orb the expansion is over a set of atomic orbitals with which mono and bicentric contributions are calculated. This new approach of MOLLYNX-orb can also be applied to nonmagnetic crystals. This paper summarizes the theoretical ground of two models and describes the first applications to organic, organometallic and inorganic magnetic materials

Phase diagram senses orbitals and prompts a fundamental constant

Van der Waals’ discovery of that the volumes of molecules and their intermolecular attraction between them cause the peculiarities of the phase diagrams of gases and liquids1 gave the greatest impact on the progress of science and industry. Unfortunately, the phase charts of solids capable to advance scientific and technical progress remain uncomprehended mystery. Only the certain linear phase boundaries are understood by the struggle of magnetic field B against the thermal agitation2,3. Here we show that the intersection volume of internal atomic orbitals determines the form of phase boundary and, furthermore, energy per unit volume of the intersection is a new fundamental constant v = 8.941 eV/Å3. Together with the known struggle contribution2,3 to TC(B), we found a term proportional to the intersection volume of 3deg and 2p orbitals in the Sm0.55Sr0.45MnO3 manganite. Hysteresis of TC is described by the avalanche-like widening of the intersection volume due to reducing the Coulomb distortion with double-exchange ferromagnetism. The pressure-TC diagram4 of (Sm1-xNdx)0.55Sr0.45MnO3 (x=0, 0.2, 0.4, 0.5) is approximated with the same parameters as the TC(B) diagram of Sm0.55Sr0.45MnO3. Furthermore, the diamond’s melting point 4157oC calculated from the intersection volume of sp3-orbitals is in excellent agreement with the real 4000oC. Tips explaining the puzzling pressure-TN diagrams5-10 of NiS, Ni1-xS1-ySey, BaVS3, V2O3, RNiO3 and ferrites were given. Our discovery is the beginning of condensed-matter geometrodynamics and marks an era of studying phase diagrams to advance condensed-matter physics and tailor new materials with predicted properties necessary in sunrise industries. Moreover, internucleon, interquark and intergluon orbital intersections would be useful for understanding the properties of nuclei, nucleons and quarks.