The energy of fcc and hcp foams

ABSTRACTWe outline a modern theory of the spontaneous polarization P in pyroelectric and ferroelectric materials. Although P itself isnot an observable, the difference ΔP between two crystal states can indeed be measured and calculated. We define P as the difference between the polar structure and a suitably chosen nonpolar prototype structure. We previously proposed and implemented a supercell scheme in order to evaluate P in pyroelectric BeO; here we adopt an approach recently developed by King-Smith and Vanderbilt, where ΔP is obtained from the computation of Berry's phases, with no use of supercells. We apply this novel approach, which is numerically very convenient, in order to revisit our previous work on BeO. We then perform a first-principles investigation of the spontaneous polarization P of KNbO3 in its tetragonal phase, which is a well studied perovskite ferroelectric. Our calculated P value confirms the most recent experimental data. The polarization is linear in the ferroelectric distortion; the Born effective charges show strong variations from nominal ionic values, and a large inequivalence of the 0 ions. Only the highest nine valence-band states (O 2p) contribute to P, while all the other states behave as rigid core states.

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Electron-Phonon Coupling Strength of Specific Phonons from First Principles Lapw Calculations

MRS Proceedings ◽

10.1557/proc-141-165 ◽

1988 ◽

Vol 141 ◽

Cited By ~ 3

Author(s):

H. Krakauer ◽

R. E. Cohen ◽

W. E. Pickett

Keyword(s):

Coupling Strength ◽

First Principles ◽

Mode Coupling ◽

Local Density ◽

Matrix Elements ◽

Dual Representation ◽

Electron Phonon Interaction ◽

Electron Phonon Coupling ◽

Coupling Strengths ◽

The Difference

AbstractElectron-phonon matrix elements, phonon linewidths and mode coupling strengths are being calculated for La2-xMxCuO4 (M-divalent cation, for paramagnetic x-0.0 and for x-0.15 in a rigid band picture) from first principles local density calculations. The change in potential due to a particular phonon mode is calculated from the difference of self-consistent one-electron potentials, and appropriate Fermi surface averages are carried out for selected modes, allowing us to obtain the phonon linewidth due to the electron-phonon interaction, and the corresponding coupling strength λQ. Here we establish the numerical accuracy within the dual representation of the potential used in the Linearized Augmented Plane Wave (LAPW) method. Evaluations of phonon linewidths and mode coupling strengths are presented for Al and Nb and compared with previous information on these modes. We present preliminary results for the full matrix elements and coupling of the La2CuO4 oxygen planar X-point breathing mode, and compare with a simpler approximation.

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Prediction of Liquid Formation for Solder and Non-Solder Mask Defined Array Packages

Journal of Electronic Packaging ◽

10.1115/1.1401738 ◽

1999 ◽

Vol 124 (1) ◽

pp. 37-44 ◽

Cited By ~ 14

Author(s):

Wen-Hwa Chen ◽

Kuo-Ning Chiang ◽

Shu-Ru Lin

Keyword(s):

Solder Joint ◽

Solder Joints ◽

Reflow Process ◽

Surface Evolver ◽

Restoring Force ◽

Solder Mask ◽

The Difference ◽

Design Factors ◽

Joint Volume ◽

Liquid Formation

This study presents an efficient method to accurately predict solder joint geometry after a reflow process. The proposed method can be utilized for Solder Mask Defined (SMD), Non-Solder Mask Defined (NSMD), or C4 type solder joints. The reflow process involves several design factors capable of influencing the final shape of the molten solder joint, such as solder joint volume, restoring force, surface tension, contact angle, pad thickness, and pad size. These factors are all considered in the calculations. The computed results are compared with those using the Surface Evolver program and also with available numerical/experimental results. Their excellent agreement shows that the method developed herein can be practically applied to predict the reflow shape of SMD/NSMD solder joints. The difference between SMD and NSMD is also examined in detail. Results in this study provide designers with a fundamental guideline for accurately predicting the liquid formation of solder joints during the reflow process.

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First-Principles Study of Chemical Driving Force for Face Centered Cubic to Hexagonal Close Packed Martensitic Transformation in Hydrogen-Charged Iron

Metallurgical and Materials Transactions A ◽

10.1007/s11661-019-05237-6 ◽

2019 ◽

Vol 50 (7) ◽

pp. 3019-3023 ◽

Cited By ~ 1

Author(s):

Y. Kuroki ◽

S. Kawano ◽

S. Iikubo ◽

H. Ohtani ◽

M. Koyama ◽

...

Keyword(s):

Martensitic Transformation ◽

First Principles ◽

Driving Force ◽

Face Centered Cubic ◽

Hexagonal Close Packed ◽

First Principles Study ◽

Face Centered

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First-Principles Study of Nanofacet Formation on 4H-SiC(0001) Surface

Materials Science Forum ◽

10.4028/www.scientific.net/msf.778-780.201 ◽

2014 ◽

Vol 778-780 ◽

pp. 201-205

Author(s):

Keisuke Sawada ◽

Jun Ichi Iwata ◽

Atsushi Oshiyama

Keyword(s):

Surface Energy ◽

Total Energy ◽

First Principles ◽

Atomic Layer ◽

First Principles Calculations ◽

Atomic Structures ◽

First Principles Study ◽

Energy Variation ◽

The Difference ◽

Facet Formation

We perform the first-principles calculations on the 4H-SiC(0001) surface and clarify the mechanism of the facet formation. We first identify atomic structures of single-, double- and quadribilayer steps and find that the single-bilayer (SB) step has the lowest total energy among these three step structures. Then, we reveal that the nanofacet consisting of SB steps is more energetically stable than the equally spaced SB step and the surface-energy variation caused by the difference of stacking sequences of the bi-atomic layer near the surface is an important factor of the facet formation.

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Calculation of electronic structure and mechanical properties of DO3–Fe75-xSi25Nix intermetallic compounds by first principles

International Journal of Modern Physics B ◽

10.1142/s0217979215500873 ◽

2015 ◽

Vol 29 (13) ◽

pp. 1550087

Author(s):

R. Ma ◽

M. P. Wan ◽

J. Huang ◽

Q. Xie

Keyword(s):

Mechanical Properties ◽

Intermetallic Compounds ◽

First Principles ◽

Electronic Structures ◽

Density Functional ◽

Elastic Parameters ◽

Functional Theory ◽

Ni Content ◽

The Density Functional Theory ◽

The Difference

Based on the density functional theory (DFT), the plane-wave pseudopotential method was used to investigate the electronic structures and mechanical properties of DO 3– Fe 75-x Si 25 Ni x(x = 0, 3.125, 6.25 and 9.375) intermetallic compounds. The elastic parameters were calculated, and then the bulk modulus, shear modulus and elastic modulus were derived. The paper then focuses on the discussion of ductility and plasticity. The results show that by adding appropriate Ni to Fe 3 Si intermetallic compound can improve the ductility. But the hardness will increase when the Ni content exceeds 6.25%. Analysis of density of states (DOS) and overlap populations indicates that with the difference of the strength of bonding and activity, there were some differences of ductility among different Ni contents. The Fe 71.875 Ni 3.125 Si 25 has the lowest hardness because the covalent bonding (Fe–Si bond and Si–Ni bond) has the minimum covalent electrons.

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First-Principles Study on Elastic Anomalies in Ag/Al Multilayers

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.345-346.959 ◽

2007 ◽

Vol 345-346 ◽

pp. 959-962

Author(s):

Yusuke Kinoshita ◽

Yoshitaka Umeno ◽

Takayuki Kitamura

Keyword(s):

Electronic Structure ◽

Elastic Constant ◽

First Principles ◽

Electronic Structures ◽

Interplanar Spacing ◽

First Principles Calculation ◽

Mixing Rule ◽

Modulation Period ◽

The Difference ◽

Elastic Anomalies

Using the first-principles calculation, the elastic constant C44 of Ag/Al multilayers with different modulation periods from 0.43 nm to 2.27 nm has been evaluated in order to examine the effect of atomic and electronic structures on it. With increasing modulation period, C44 decreases and becomes close to that obtained by the conventional mixing rule, however, the difference of 8 % still remains at the modulation period of 2.27 nm. As C44 correlates with the average interplanar spacing, the decrease of C44 can be explained by the decrease of the charge density in the stacking direction due to the increase of the average interplanar spacing. The difference in the electronic structure is included in the effect of atomic structure.

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On the cubic and hexagonal close-packed lattices

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1955.0023 ◽

1955 ◽

Vol 227 (1171) ◽

pp. 447-465 ◽

Cited By ~ 70

Keyword(s):

Solid Helium ◽

Zero Point ◽

Lattice Energy ◽

Close Packing ◽

Inert Gases ◽

Zero Point Energy ◽

Point Energy ◽

Hexagonal Close Packed ◽

The Difference ◽

Central Forces

The present paper was stimulated by the discovery by Dugdale & Simon (1953) of a polymorphic transition in solid helium. A discussion is given of the relative stability of the cubic and hexagonal close-packed lattices assuming central forces of the Mie—Lennard-Jones type. Taking static lattice energy alone into account the usual laws of force favour the hexagonal close-packed lattice, the difference in energy being about 0·01%. However, lattice dynamics indicates that the equivalent Debye Θ at the absolute zero is smaller for the cubic lattice, the difference being about 1%. Hence, ignoring zero-point energy, we should expect a transition to occur from hexagonal to cubic at an elevated temperature. The estimated temperature and energy of the transition are of the same order of magnitude as those observed experimentally in solid helium. An estimate is made of the effect of zero-point energy; the results can be applied with confidence to the heavier inert gases, but can only be considered as giving a qualitative indication for helium, since anharmonic effects are of great importance in this case. For the other inert gas solids it is concluded that the experimentally observed cubic close-packing at all temperatures must be due to non-central forces.

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Manifestation of axion electrodynamics through magnetic ordering on edges of a topological insulator

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1515664112 ◽

2015 ◽

Vol 112 (37) ◽

pp. 11514-11518 ◽

Cited By ~ 7

Author(s):

Yea-Lee Lee ◽

Hee Chul Park ◽

Jisoon Ihm ◽

Young-Woo Son

Keyword(s):

Electric Field ◽

Topological Insulator ◽

Time Reversal ◽

First Principles ◽

Surface States ◽

Magnetic Ordering ◽

Crystal Face ◽

Magnetic Dipoles ◽

Topological Surface ◽

The Difference

Because topological surface states of a single-crystal topological insulator can exist on all surfaces with different crystal orientations enclosing the crystal, mutual interactions among those states contiguous to each other through edges can lead to unique phenomena inconceivable in normal insulators. Here we show, based on a first-principles approach, that the difference in the work function between adjacent surfaces with different crystal-face orientations generates a built-in electric field around facet edges of a prototypical topological insulator such as Bi2Se3. Owing to the topological magnetoelectric coupling for a given broken time-reversal symmetry in the crystal, the electric field, in turn, forces effective magnetic dipoles to accumulate along the edges, realizing the facet-edge magnetic ordering. We demonstrate that the predicted magnetic ordering is in fact a manifestation of the axion electrodynamics in real solids.

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