Embedded Cluster Model: Application to Molecular Crystals

2003 ◽  
Vol 800 ◽  
Author(s):  
Maija M. Kuklja ◽  
Frank J. Zerilli ◽  
Peter Sushko
Keyword(s):  
Multiscale Modeling ◽  
Cluster Model ◽  
Molecular Crystals ◽  
Hydrostatic Compression ◽  
Structure And Properties ◽  
Cluster Approach ◽  
Model Application ◽  
Hartree Fock ◽  
Structure Calculations ◽  
Crystal Structure Calculations

ABSTRACTMultiscale modeling using an embedded cluster approach is presented and applied to study the structure and properties of molecular crystals. We discuss the results of hydrostatic compression modeling of 1,1-diamino-2,2-dinitroethylene obtained with the embedded cluster model and the Hartree-Fock method and compare these with the full periodic crystal structure calculations. Details of the electronic structure of the perfect, highly compressed material are discussed. The results demonstrate the applicability of the embedded cluster model. We show that the band gap of the perfect material is not sensitive to hydrostatic compression, but some changes induced by the pressure take place in the valence band.

Hyperfine Interactions on Magnetic Ions Nuclei in Titanates

2014 ◽  
Vol 215 ◽  
pp. 109-112
Author(s):  
Polina A. Agzamova ◽  
Yulia V. Leskova ◽  
Anatoliy E. Nikiforov
Keyword(s):  
Field Theory ◽  
Experimental Data ◽  
Cluster Model ◽  
Hyperfine Interactions ◽  
Cluster Approach ◽  
Crystal Field Theory ◽  
Hartree Fock ◽  
Magnetic Ions ◽  
Hyperfine Interaction Parameters ◽  
Better Than

The electric and magnetic hyperfine interaction parameters (υQ, η, Hc) on 47,49Ti nuclei in lanthanum and yttrium titanates were calculated in the cluster model by the unrestricted Hartree-Fock method. The calculation in the cluster approach describes the experimental data better than that in the frameworks of LDA and LDA+U model and modern crystal-field theory.

scholarly journals RELATIVE MOTION CORRECTION TO FISSION BARRIERS

2008 ◽  
Vol 17 (01) ◽  
pp. 151-159 ◽  
Author(s):  
J. SKALSKI
Keyword(s):  
Relative Motion ◽  
Cluster Model ◽  
Motion Correction ◽  
Mean Field Theory ◽  
Mean Field ◽  
Ternary Fission ◽  
Skyrme Interaction ◽  
Hartree Fock ◽  
Fission Barriers ◽  
The Mean

We discuss the effect of kinetic energy of the relative motion becoming spurious for separate fragments on the selfconsistent mean-field fission barriers. The treatment of the relative motion in the cluster model is contrasted with the necessity of a simpler and approximate approach in the mean-field theory. A scheme of the energy correction to the Hartree-Fock is proposed. The results obtained with the effective Skyrme interaction SLy 6 show that the correction, previously estimated as ~ 8 MeV in A = 70 - 100 nuclei, amounts to 4 MeV in the medium heavy nucleus 198 Hg and to null in 238 U . However, the corrected barrier implies a shorter fission half-life of the latter nucleus. The same effect is expected to lower barriers for multipartition (i.e. ternary fission, etc) and make hyperdeformed minima less stable.

Hartree-Fock polymer band-structure calculations with general atomic functions

1997 ◽  
Vol 55 (4) ◽  
pp. 2079-2088
Author(s):  
J. D. Talman ◽  
J.G. Fripiat ◽  
J. Delhalle
Keyword(s):  
Band Structure ◽  
Hartree Fock ◽  
Band Structure Calculations ◽  
Structure Calculations

Unusual Bonding in Ternary Nitrides: Preparation, Structure and Properties of Ce2MnN3.

1998 ◽  
Vol 53 (1) ◽  
pp. 63-74 ◽  
Author(s):  
Rainer Niewa ◽  
Grigori V. Vajenine ◽  
Francis J. DiSalvo ◽  
Haihua Luob ◽  
William B. Yelon
Keyword(s):  
Electrical Resistivity ◽  
Three Dimensional ◽  
Structure And Properties ◽  
Electronic Effects ◽  
Nitrogen Gas ◽  
Metallic Behavior ◽  
Band Structure Calculations ◽  
Dimensional Network ◽  
Square Planar ◽  
Structure Calculations

Ce2MnN3 was prepared by reaction of cerium nitride and manganese with nitrogen gas at 900 °C. It crystallizes isotypic to AC2MN3 (Ac = U, Th; M = Cr, Mn) and Ce2CrN3, space group Immm (No. 71), a = 3.74994(6) Å, b = 3.44450(6) Å and c = 12.4601(2) Å. The manganese atoms are coordinated in a nearly square planar fashion by four nitrogen atoms. These corner-connected MnN4 units form infinite 1∞[MnN2N2/2] chains, which run parallel to each other along the crystallographic a-axis, forming the motif of hexagonal rod packing. Cerium atoms connect the chains into a three-dimensional network. The results of measurements of the magnetic susceptibility, as well as of the electrical resistivity suggest metallic behavior. Electronic effects leading to shorter bonds between manganese and bridging nitrogen atoms than between manganese and terminal nitrogen atoms in the 1∞[MnN2N2/2] chains were investigated through extended Hückel and LMTO band structure calculations. Issues pertaining to stability of this and some other nitridometallate structures are discussed.

scholarly journals Numerical Procedures for Relativistic Atomic Structure Calculations

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 85
Author(s):  
Charlotte Froese Fischer ◽  
Andrew Senchuk
Keyword(s):  
Variational Methods ◽  
Atomic Structure ◽  
Finite Differences ◽  
Heavy Elements ◽  
Transition Rates ◽  
Numerical Accuracy ◽  
Hartree Fock ◽  
Atomic Structure Calculations ◽  
Structure Calculations

Variational methods are used extensively in the calculation of transition rates for numerous lines in a spectrum. In the GRASP code, solutions of the multiconfiguration Dirac–Hartree–Fock (MCDHF) equations that optimize the orbitals are represented by numerical values on a grid using finite differences for integration and differentiation. The numerical accuracy and efficiency of existing procedures are evaluated and some modifications proposed with heavy elements in mind.

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