Ab initio Calculations of the Electric Field Gradients in Solids in Relation to the Charge Distribution

1992 ◽  
Vol 47 (1-2) ◽  
pp. 197-202 ◽  
Author(s):  
Karlheinz Schwarz ◽  
Peter Blaha
Keyword(s):  
Electric Field ◽  
Electronic Charge ◽  
Full Potential ◽  
Electric Field Gradients ◽  
Electronic Charge Density ◽  
Polarization Effects ◽  
Field Gradients ◽  
Band Structure Calculations ◽  
Flapw Method ◽  
Structure Calculations

AbstractA first principles method for the computation of electric field gradients (EFGs) is illustrated for various solids. This scheme is based on self-consistent energy band-structure calculations by the full potential linearized augmented plan wave (FLAPW) method which provides the electronic charge density including all polarization effects. By numerically solving Poisson's equation we obtain the Coulomb potential in a form which allows to compute the EFG directly. Our method is demonstrated for insulators (Cu2O), metals (hcp-Zn), supercondutors (YBa2Cu3O7 ) and molecular crystals (Cl2, Br2 , I2).

The Breathing Mode of BaBiO3: Electric Field Gradient and Total Energy Calculations

1994 ◽  
Vol 49 (1-2) ◽  
pp. 129-132 ◽  
Author(s):  
P. Blaha ◽  
K. Schwarz ◽  
P. Dufek ◽  
G. Vielsack ◽  
W. Weber
Keyword(s):  
Electric Field ◽  
Full Potential ◽  
Electric Field Gradients ◽  
Augmented Plane Wave ◽  
Breathing Mode ◽  
Field Gradients ◽  
Total Energies ◽  
Linearized Augmented Plane Wave ◽  
Structure Calculations ◽  
Oxygen Site

Abstract We present ab initio full-potential linearized augmented plane wave (LAPW) band structure calculations for BaBiO3. We focus on total energies and electric field gradients at the oxygen site and present results for the breathing mode in the experimentally observed cubic and monoclinic structures of doped and undoped Ba1-xKxBiO3.

Rare earth borocarbides: Electronic structure calculations and electric field gradients

2000 ◽  
Vol 62 (10) ◽  
pp. 6774-6785 ◽  
Author(s):  
M. Diviš ◽  
K. Schwarz ◽  
P. Blaha ◽  
G. Hilscher ◽  
H. Michor ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Rare Earth ◽  
Electric Field ◽  
Electronic Structure Calculations ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
Structure Calculations

Electric Field Gradient Calculations of Various Borides

1996 ◽  
Vol 51 (5-6) ◽  
pp. 527-533 ◽  
Author(s):  
K. Schwarz ◽  
H. Ripplinger ◽  
P. Blaha
Keyword(s):  
Electric Field ◽  
First Principles ◽  
Density Functional ◽  
The Self ◽  
Full Potential ◽  
Electric Field Gradients ◽  
Charge Density Distribution ◽  
Functional Theory ◽  
Field Gradients ◽  
Self Consistent

Abstract A first-principles method for the computation of electric field gradients (EFG) is illustrated for various borides. It is based on energy band calculations using the full-potential linearized aug-mented plane wave (LAPW) method within density functional theory. From the self-consistent charge density distribution the EFG is obtained without further approximations by numerically solving Poisson's equation. The dependence of the EFG on structure, chemical composition or substitution is demonstrated for the diborides MB2 (with M = Ti, V, Cr, Zr, Nb, Mo, and Ta), the hexaborides (CaB6, SrB6 and BaB6) and boron carbide which is closely related to α-boron.

scholarly journals Investigation of the Negative Thermal Expansion of ZrW2O8

2000 ◽  
Vol 55 (1-2) ◽  
pp. 301-310 ◽  
Author(s):  
N. Ulbrich ◽  
W. Tröger ◽  
T. Butz ◽  
P. Blaha
Keyword(s):  
Thermal Expansion ◽  
Electric Field ◽  
Negative Thermal Expansion ◽  
Temperature Structure ◽  
Full Potential ◽  
Electric Field Gradients ◽  
Quadrupole Interactions ◽  
Nuclear Quadrupole Interactions ◽  
Field Gradients ◽  
Nuclear Quadrupole

The negative thermal expansion in ZrW2O8 was investigated on a microscopic scale by temperature dependent measurements of the electric field gradients at the nuclear probe 187W(β-) 187Re using time differential perturbed angular correlation spectroscopy. Two distinct nuclear quadrupole interactions I VzzRe1 l= 18.92(4) • 10 21 V/m2 , ηRe1 = 0.0 and I VzzRe1 l = 4.55(2) • 1021 V/m2 , ηRe1 = 0.053(3) were observed at 295 K, which are assigned to the two crystallographically distinct W0 4 tetrahedra of the room temperature structure. Ab initio calculations of electron densities and electric field gradients with 1:7 Re-impurities using the full potential linearized augmented plane wave package WIEN97 yield the electric field gradients VzzRe1 = 12.63 • 10 21 V/m2 , ηRe1 = 0.0 and VzzRe2 =4.90 • 10 21 V/m2 , ηRe2 =0.0. The observed temperature dependence of the nuclear quadrupole interactions agrees well with the structural phase transition at 428 K observed by neutron and x-ray diffraction. Our experiments corroborate the suggested mechanism of coupled librations of rigid ZrO6 octahedra and WO4 tetrahedra, which is an alternative description of transverse vibrations of oxygen atoms in Zr-O-W bonds, for the negative thermal expansion in ZrW2 O8

Electric Field Gradients Around Point Defects in Metals

1996 ◽  
Vol 51 (5-6) ◽  
pp. 489-505
Author(s):  
Alfred Seeger ◽  
Jörg Ehmann ◽  
Manfred Fähnle
Keyword(s):  
Electric Field ◽  
Ab Initio ◽  
Density Functional ◽  
Local Density ◽  
Energy Levels ◽  
Full Potential ◽  
Good Resolution ◽  
Quadrupole Moments ◽  
Electric Field Gradients ◽  
Field Gradients

The splittings of nuclear energy levels caused by the electric field gradients acting on the quadrupole moments of nuclei in the neighbourhood of atomic defects in cubic metals may serve as ‘‘fingerprints’’ providing us with a unique characterization of these defects. In favourable cases the NQDOR technique (n̲uclear q̲uadrupole d̲ouble r̲esonance) permits sensitive measurements of these splittings with good resolution. The present paper outlines the status of the ab-initio calculation of electric field gradients with emphasis on the theoretical basis (density functional theory with local density approximation) and on the techniques required for handling the specific problems associated with defects. Recent work by the supercell approach on atomic defects in Al and Cu, making use either of the full-potential linearized augmented-plane-wave method or of the ab-initio pseudopotential method, are reported and compared with experiments. The excellent agreement between experiment and theory for the field gradients acting on the nearest-neighbour nuclei of monovacancies in Al demonstrates the reliability and the potential of the theory.

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