Intra-atomic Correlation Research Articles

All-valence electron investigation of Cn binding energies (n?60)

We present a theoretical study of the electronic properties of some Cn aggregates : C3, C20, C24, C28, C60 ; C3 is linear, the others are polyhedrons. Our calculation includes all the valence electrons. A one-electron description is first developed, then we include intraatomic correlations by using a second order perturbative treatment introduced by J. Friedel for sp v hybridized systems.

Anisotropic charge transfer between hydrogenic states and a metallic substrate.

By measuring the angular distribution of photon emission from desorbed excited atoms it is possible to measure the anisotropy in charge-transfer rates between metallic states and the oriented excited states outside of the surface. The measured anisotropy of 2.5 shows excellent agreement with the calculated value of 2.54 and clearly demonstrates that intra-atomic correlation effects must be taken into account when describing charge transfer.

Exchange interaction in f electron systems: low carrier magnetic systems

Anomalous properties found in low carrier magnetic systems are discussed. Problems in various low carrier f electron systems are reviewed. The p-f exchange model proposed previously for CeSb is extended to include the many-body strong correlation effect, both for the short-range intra-atomic correlation effect and the long-range Coulomb effect, known to cause Wigner crystals. It is shown that various anomalous properties found recently for very pure single crystals of La monopnictides and Ce monopnictides are well explained by the above model. As new states, Wigner crystal liquid, neutral magnetic polaron lattice and Γ 8-bound p states have emerged.

INTERACTION BETWEEN O QUASIPARTICLES IN CuO2-BASED SUPERCONDUCTORS

We consider the extended Hubbard model including repulsion Upd between nearest-neighbor Cu and O holes. In the limit of strong intra-atomic correlations and weak hopping, we derive an effective Hamiltonian for the O holes. This Hamiltonian contains interactions between O holes with a common nearest-neighbor Cu ion. The effective interaction between two holes is repulsive for small Upd and attractive otherwise. Bound states between two holes exist only if the effective interaction between them is sufficiently large and negative.

Size effect in3He n aggregates. A Gutzwiller approach

The Hubbard hamiltonian (where only intraatomic correlations between fermions are taken into account) is particularly well suited for the description of3He systems. It has already been used in the description of point defects (such as spin polarons) in the bulk. The variational Gutzwiller method is one of the most useful way for treating the Hubbard hamiltonian. This technique has been applied with success by Vollhardt to the bulk. We apply it here to aggregates. Our main results are the following: 1 existence of a critical size,Nc, above which3Hen begin to be stable; 2 calculation of the magnetic susceptibility. In this part two cases are studied: low magnetic field where only the density of states, σ(EF), at the Fermi level is needed and high magnetic field where the whole density of states is needed. The results are compared with other theoretical calculations.

Estimation of electronic correlation energies and binding energies for molecules composed of first-row atoms

The interatomic and intra-atomic correlation energies are calculated for a number of molecules composed of first-row atoms. This is done by starting from an ab initio SCF calculation and by treating the correlations with the help of local operators. The main result is the derivation of simple analytic formulae which fit rather well the results of the numerical computations. They depend only on the type of the chemical bond, the bond lengths and the Mullikan populations of the different atoms.

Derivation of a master equation for charge-transfer processes in atom-surface collisions.

The time-dependent Anderson model for multiple levels interacting with a continuum is studied using the slave-boson Green's-function technique, with an eye to understanding charge-transfer phenomena for an atomic species moving outside a metallic surface. It is shown that in the finite-temperature and low-velocity limit, the equations for the occupation numbers satisfy a master equation. Application to charge-exchange processes in atom-surface-scattering experiments shows that the presence of strong intra-atomic correlation effects can drastically change the charge-transfer dynamics.

Symmetry-adapted perturbation theory calculation of the intra-atomic correlation contribution to the short-range repulsion of helium atoms

The first-order exchange energy in the interaction of two helium atoms is expanded as a double-perturbation series with respect to the Moller–Plesset-type fluctuation potentials for the isolated atoms. The resulting perturbation corrections have been calculated using orbital basis sets of varying size. Results in our largest [7s4p2d1f] basis are compared with an accurate value of the first-order energy computed using Gaussian-type geminals. It is shown that the Moller–Plesset-type expansion for the exchange repulsion energy converges moderately fast and that the major part of the intra-atomic correlation correction to the first-order exchange energy is due to one-particle correlation effects included in the Brueckner orbitals.

Simple rules for electronic correlation energies in hydrocarbon molecules

Simple expressions were derived which fit ab initio results for the inter- and intra-atomic correlation energy contributions of a number of hydrocarbon molecules. They depend on the type of bond, bond length and Mulliken population analysis data only. A comparison is made between the present results and previous ones, which were not based on ab initio calculations.

High energy magnetic neutron scattering in heavy fermion compounds

High energy magnetic inelastic neutron scattering measurements of intermultiplet transitions in rare earth and actinide metals have established the importance of intra-atomic correlations even in the presence of strong hybridisation. Well-defined transitions are observed up to an energy of 1766 meV in thulium metal. The 3H 4→ 3F 2 transition is observed across the alloy series U(Pd 1− x Pt x ) 3, showing that localized 5f 2 excitations persist in the heavy fermion compound UPt 3. The splitting of the spin-orbit transition in CeAl 3 suggests that hybridisation is an important component in the crystal field potential.

A model for divalent-atom systems-one dimension

A one-dimensional system, with L sites and periodic boundary conditions, is considered. N divalent atoms occupy sites. The atoms have two orbitals, electron hopping is allowed between nearest neighbour atoms, and intra-atomic electron correlation is taken into account. The ground and first excited many-body states are estimated using a basis, appropriate to weak interatomic coupling, in which multiple nearest neighbour resonating valence bond excitations, appropriately symmetrised, are included. Ordered and disordered systems are considered, for large L.

Model for a system of divalent atoms

A one-dimensional system is considered with L sites and periodic boundary conditions. The atoms on the sites have two orbitals, electron hopping is allowed to nearest neighbors and intra-atomic electron correlation energies are included. The ground and first excited many-body states for the divalent atom system are calculated using a basis, appropriate for weak interatomic coupling, in which multiple nearest neighbor resonating valence bond states, appropriately symmetrized, are included. The system is found to be insulating in the large L limit.

A Possible Pairing Mechanism for High-TcSuperconductivity

We propose a probable pairing mechanism for high- T c superconductors. The strong correlation between intra-atomic Cu–d holes, U , is treated exactly. We assume holes introduced by doping occupy O–p π as well as O–p σ orbits, and p π holes become itinerant. Strong intra-atomic correlation V , between p π - and p σ -holes, and the Hubbard U can lead to an attractive force between O–p π itinerant holes.

Many-body effects in electron spectroscopies from absorbates

The density-density correlation function and the one-electron Green function of the one-impurity Anderson Hamiltonian are found by the lattice configuration approach, a modification of the resolvent method, recently proposed by the authors. In this approach, the matrix elements of the resolvent operator, R( z) = ( z − H) −1, between suitably chosen many-electron sttes of N, N + 1 or N − 1 particles are put in correspondence with the sites of a rectangular lattice. The chosen many-electron states (configurations) diagonalize H in the absence of hopping ( V = 0) and contain the full intra-atomic correlation ( U) in the doubly-occupied configurations. It turns out that matrix elements between highly-excited configurations, with many electron-hole pairs, can be expressed in terms of matrix elements without electron-hole pairs. This allows doing the calculation by solving a self-consistency matrix equation in a highly reduced basis. The calculated spectral densities are in good agreement with energy-loss, photoemission and inverse photoemission spectra of hydrogen adsorbed on nickel.

Correlation Effects of Third-order Perturbation in the Extended Hubbard Model

Using the local approach, we have performed a third�order perturbation calculation to investigate the effects of intra-atomic electron correlation and electron and spin correlation between nearest neighbour sites in the extended Hubbard model. We found that significant correction of the third order over the second order results and, in comparison with the results of the third-order perturbation where only the intra-atomic electron correlation is included, the influence of the electron and spin correlation between nearest neighbour sites on the correlation energy is non-negligible.

LOCAL APPROACH IN THE HUBBARD MODEL

Based on the intraatomic electron correlation and the interatomic electron and spin correlation, the local approach has been used to the Hubbard model. The term〈OOH〉which was neglected in the general calculation is retained in our calculation. Camparing our results with those of the general calculation, we find that when U is large, the effects of the term〈OOH〉in the paramagnetic phase can not be heglected for calculating the correlation energy, the ground state energy, the local moments and the antiferromagnetic polarization around the local moments. To estimate more accurately the electron correlation effects, one has to calculate to higher orders and check he convergency of the series.

The screened intra-atomic correlation energy in transition-metal oxides

An attempt has been made to calculate the screened intra-atomic Coulomb repulsion, based on a study of charge transfer due to covalent hybridisations between 3d and 2p levels. An expression has been found and applied to VO2, V2O3 and Ti2O3. Good quantitative agreement is obtained with previous estimates.

LOCAL APPROACH TO VARIATIONAL METHOD FOR ELECTRON CORRELATION IN NARROW BAND SYSTEMS

Using the local approach, we have performed a third order perturbation calculation to investigate the electron correlation effect in extended Hubbard model with both positive and negative intraatomic and interatomic correlation energies. We found the significant third order correction over the second order terms. Consequently, all published results, especially the phase diagrams which were derived with the second order perturbation calculation are not reliable.

Electronic polaron effects in heavy-electron materials.

It is shown that intra-atomic Coulomb correlation causes the f electrons in heavy-fermion materials to propagate like polarons in insulators and semiconductors. The effective mass of the quasiparticles is enhanced, and at finite temperatures the quasiparticles are damped so that the polaron effect may be a contributing factor to the crossover from coherent behavior at low temperatures to single-site behavior at high temperatures.

Intraatomic correlation effects for the He–He dispersion and exchange–dispersion energies using explicitly correlated Gaussian geminals

The coupling of the intermolecular interaction with the intramolecular correlation effects is considered using the coupled cluster (CC) formalism. The CC equations for the dispersion energy are presented and their relation to the double perturbation theory is analyzed. An approximate scheme based on partial decoupling of the CC equations is applied for the He–He interaction. Numerical results are obtained using explicitly correlated Gaussian geminal basis set. They confirm the importance of the intraatomic (apparent) correlation effects and agree very well with the experimentally derived potential.