Internal rotations of the methyl group in ortho-substituted and 2,6-disubstituted toluenes in their ground state have been investigated by means of various ab initio quantum chemistry methods. Computed barriers at the Hartree-Fock (HF) level using medium sized basis sets agreed reasonably with experimental results in the case of the studied ortho-substituted toluenes. However, this agreement wo...

Ab initio periodic Hartree-Fock (HF) theory was used to determine the elastic constants and selected phonon frequencies of bulk MgO; the accuracy of a posteriori correlation corrections to the periodic Hartree-Fock calculations is also discussed. Inc)usion of difFuse atomic orbitals in the MgO basis was necessary to accurately describe elastic distortions and phonon vibrations of the solid. The...

The problem of electron motion in an arbitrary field of nuclei is an important quantum mechanical problem finding applications in many diverse fields. From the variational principle we derive a procedure, called the Hartree-Fock (HF) approximation, to obtain the many-particle wavefunction describing such a system. Here, the central physical concept is that of electron indistinguishability: whil...

BACKGROUND Recurrent hospital admissions are common among patients admitted for acute decompensated heart failure (ADHF), but identification of patients at risk for rehospitalization remains challenging. Contemporary heart failure (HF) management programs have shown modest ability to reduce readmissions, partly because they monitor signs or symptoms of HF worsening that appear late during decom...

Introduction: The time scale and functional shape of Earth’s accretion and core formation may be investigated using the Hf (half-life: 9 Myr)-W extinct nuclide chronometer [1,2] because the Hf/W ratio is fractionated both strongly and uniquely by core formation. W is partitioned into the metal phase and Hf into the silicate mantle during the formation of the Earth. The core will develop a defic...

Crossed molecular beam experiments and accurate quantum dynamics calculations have been carried out to address the long standing and intriguing issue of the forward scattering observed in the F + H(2) --> HF(v' = 3) + H reaction. Our study reveals that forward scattering in the reaction channel is not caused by Feshbach or dynamical resonances as in the F + H(2) --> HF(v' = 2) + H reaction. It ...

Space weather effects can strongly influence high-frequency (HF) communications by changing the ionospheric environment through which the radio waves propagate. Since many systems utilize HF communications, the ability to make real-time assessments of propagation conditions is an important part of space weather monitoring systems. In this paper, we present new techniques for measuring high-lati...

In this paper, we present the first correlated ab initio investigations on the ground electronic state of the O(2)-HF complex. Calculations were performed using the CCSD(T) method with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. The results show that there are two equivalent minimum energy hydrogen-bonded structures of planar bent geometry, where the minima correspond to exchange of the oxygen ...

Recent experimental discoveries of two-dimensional (2D) magnets have triggered intense research activities to search for atomically thin magnetic systems. Using first-principles calculations, we predict the emergence 2D magnetism in monolayers (MLs), few layers, and surfaces nonmagnetic layered electrides ${\mathrm{Hf}}_{2}X$ $(X=\text{S}, \mathrm{Se}, \mathrm{Te})$ consisting three-atom-thick ...

A very accurate, (HF)$_2$ potential energy surface (PES) is constructed based on \ai\ calculations performed using the MOLPRO package at CCSD(T) level of theory with an aug-cc-pvQz-F12 basis set about 161~000 points. a higher correlation correction computed CCSDT(Q) for 2000 points and considered alongside other more minor corrections due to relativity, core-valence Born-Oppenheimer failure. Th...