Multiplicity of symmetry-broken Hartree-Fock solutions in multiple bonds and atomic clusters: An asymptotic view

1989 ◽  
Vol 39 (3) ◽  
pp. 981-991 ◽  
Author(s):  
M. B. Lepetit ◽  
J. P. Malrieu ◽  
M. Pelissier
2019 ◽  
Vol 14 ◽  
pp. 191
Author(s):  
K. Ch. Chatzisavvas ◽  
Ch. C. Moustakidis ◽  
C. P. Panos

The universal property for the information entropy S = a + h In Ζ is verified for atoms using a systematic study with Roothaan-Hartree-Fock (RHF) wave functions with atomic number Ζ — 2 — 54. The above relation was proposed previously for atoms, nuclei, atomic clusters and correlated atoms in a trap. Kullback-Leibler relative entropy Κ and Jensen-Shannon divergence J are employed to compare RHF with Thomas-Fermi (TF) density of atoms as well as another phenomenological density obtained by Sagar et al. Two-body density distributions in position- and momentum-space are used to calculate and compare the corresponding information entropies for correlated and uncorrelated nuclei and bosonic systems (correlated atoms in a trap). It is seen that short-range correlations (SRC) increase the values of S. One-body information entropy entropy S\ is compared with two-body information entropy and a conjecture is made for TV-body information entropy SN- The entropy Κ and the divergence J are also used to evaluate the information distance between correlated and uncorrelated densities both at the one- and the two-body levels for nuclei and trapped Bose gases.


1989 ◽  
Vol 130 (1-3) ◽  
pp. 229-239 ◽  
Author(s):  
M.B. Lepetit ◽  
J.P. Malrieu ◽  
G. Trinquier

2005 ◽  
Vol 906 ◽  
Author(s):  
Liudmila A. Pozhar ◽  
Alan T. Yeates ◽  
Frank Szmulowicz ◽  
William C. Mitchel

AbstractThe Hartree-Fock (HF) method is used to synthesize virtually (i.e., fundamental theory-based, computationally) small stable atomic clusters of Ga and In with As and V, and an In-based cluster with As and Mn. The electronic energy level structures (ELSs), optical transition energies (OTEs), and charge/spin density distributions of these clusters have been analyzed. It has been shown that the spin of such clusters is collectivized, and that this collectivization is responsible for a dramatic drop in the clusters’ OTEs as compared to those of similar pyramidal clusters that do not contain “magnetic” atoms.


2008 ◽  
Vol 8 (12) ◽  
pp. 6593-6597
Author(s):  
J. M. Montejano-Carrizales ◽  
P. G. Alvarado-Leyva ◽  
E. M. Sosa-Hernandez

The magnetic properties of a pair V4 atomic clusters embedded in bulk Fe are determined by using a realistic spd-band Hubbard-like model. The spin density distribution is calculated self-consistenly in the unrestricted Hartree-Fock approximation. The local magnetic moments μ(i) are obtained at various atoms i of the cluster and of the surrounding Fe matrix. We consider two different geometrical arrangements for V clusters, collinear (C) and non-collinear (NC). In all the cases studied the magnetic coupling in the interface cluster-matrix is antiferromagnetic, and the ferromagnetic order of the matrix is not broken by the presence of the V atoms, although the local magnetic moments of Fe atoms at the interface cluster-matrix, are reduced respect to Fe bulk magnetization (2.22 μB) about 8%–20%. We compare the results with those of just one V4 atomic cluster embedded in bulk Fe.


2009 ◽  
Vol 1198 ◽  
Author(s):  
Liudmila A Pozhar ◽  
Constantine Mavromichalis

AbstractElectronic and magnetic properties of small Co-O atomic clusters (“quantum wires”) have been studied in the framework of the Hartree-Fock (HF) method. The obtained results indicate that non-stoichiometric Co - O molecules with more than two O atoms possess at least one remarkably stretchable O-O bond that may facilitate significant re-construction of such molecules to larger structures. This re-construction may result in energetically favorable spin re-alignment in “antiferromagnetic” HF singlet Co-O molecules converting the singlets to larger “ferromagnetic” HF triplets and pentets. Such a spin re-alignment is energetically favorable, and may happen at the antiferromagnet-ferromagnet interface in “critical” core (Co) – shell (CoO) exchange-biased nanoclusters, providing for minimization of the surface energy, and leading to a loss of exchange bias. The obtained results are in agreement with available experimental and computational data.


Author(s):  
J. Taft∅

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.


Author(s):  
Wah Chi

Resolution and contrast are the important factors to determine the feasibility of imaging single heavy atoms on a thin substrate in an electron microscope. The present report compares the atom image characteristics in different modes of fixed beam dark field microscopy including the ideal beam stop (IBS), a wire beam stop (WBS), tilted illumination (Tl) and a displaced aperture (DA). Image contrast between one Hg and a column of linearly aligned carbon atoms (representing the substrate), are also discussed. The assumptions in the present calculations are perfectly coherent illumination, atom object is represented by spherically symmetric potential derived from Relativistic Hartree Fock Slater wave functions, phase grating approximation is used to evaluate the complex scattering amplitude, inelastic scattering is ignored, phase distortion is solely due to defocus and spherical abberation, and total elastic scattering cross section is evaluated by the Optical Theorem. The atom image intensities are presented in a Z-modulation display, and the details of calculation are described elsewhere.


Author(s):  
A. M. Bradshaw

X-ray photoelectron spectroscopy (XPS or ESCA) was not developed by Siegbahn and co-workers as a surface analytical technique, but rather as a general probe of electronic structure and chemical reactivity. The method is based on the phenomenon of photoionisation: The absorption of monochromatic radiation in the target material (free atoms, molecules, solids or liquids) causes electrons to be injected into the vacuum continuum. Pseudo-monochromatic laboratory light sources (e.g. AlKα) have mostly been used hitherto for this excitation; in recent years synchrotron radiation has become increasingly important. A kinetic energy analysis of the so-called photoelectrons gives rise to a spectrum which consists of a series of lines corresponding to each discrete core and valence level of the system. The measured binding energy, EB, given by EB = hv−EK, where EK is the kineticenergy relative to the vacuum level, may be equated with the orbital energy derived from a Hartree-Fock SCF calculation of the system under consideration (Koopmans theorem).


Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.


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