FIRST PRINCIPLES CALCULATIONS OF THE ADSORPTION OF GROUP III METALS ON Si(001) AT HIGH TEMPERATURE

2002 ◽  
Vol 09 (05n06) ◽  
pp. 1641-1644 ◽  
Author(s):  
J. COTZOMI-PALETA ◽  
GREGORIO H. COCOLETZI ◽  
NOBORU TAKEUCHI
Keyword(s):  
High Temperature ◽  
Total Energy ◽  
Surface Reconstruction ◽  
High Temperatures ◽  
First Principles ◽  
Structural Parameters ◽  
First Principles Calculations ◽  
Atomic Configuration ◽  
Energy Calculations ◽  
Group Iii

First principles total energy calculations are performed to investigate the Si(001)-(3 × 4) reconstruction induced by the adsorption of group III metals (Ga, Al and In) when deposited at high temperatures. We have considered different models in our study and we have found that the pyramid-like structure proposed by Bunk et al. for In on Si(001) yields the most stable atomic configuration in all cases. We present a detailed description of this surface reconstruction, and compare the structural parameters for Al, Ga and In.

Understanding The Nb-Ti-A1 System: First Principles Calculations

1994 ◽  
Vol 364 ◽  
Author(s):  
Michael J. Mehl
Keyword(s):  
High Temperature ◽  
Bulk Modulus ◽  
Total Energy ◽  
Crystal Structures ◽  
Lattice Constant ◽  
Density Of States ◽  
First Principles ◽  
First Principles Calculations ◽  
Electronic Density ◽  
Cubic Phases

AbstractThe discovery of ductile cubic phases in the Nb-Ti-Al system has led to increased study of these high-temperature intermetallics. I have performed first-principles calculations for ordered crystal structures in this system, paying particular attention to the Nb7Ti7Al2 structure. Somewhat surprisingly, the electronic density of states, lattice constant, and bulk modulus are nearly independent of the ordering of these materials, even though the changes in the total energy are significant.

Migration of Aluminum Atoms in the Transformation of γ–to θ–Alumina

2002 ◽  
Vol 731 ◽  
Author(s):  
Shu-Hui Cai ◽  
Karl Sohlberg
Keyword(s):  
Aluminum Oxide ◽  
Total Energy ◽  
First Principles ◽  
Conversion Rate ◽  
Metastable Phases ◽  
Thermal Dehydration ◽  
First Principles Calculations ◽  
Energy Calculations ◽  
Domain Boundaries ◽  
Transformation Pathways

Abstractγ– and θ–alumina are two metastable phases of aluminum oxide observed along the thermal dehydration sequence of boehmite before conversion to the final product α–alumina. The transformation from γ– to θ–alumina was studied by using Al16O24 cells. Motion of some Al atoms from their γalumina positions to new positions and no O motions result in an approximate structure that, upon relaxation by first-principles calculations, becomes the known θ–alumina structure. Total-energy calculations along the paths of the atomic motions have been used to map out transformation pathways. The model accurately predicts experimentally observed domain boundaries in θ–alumina and the γ– to θ–alumina conversion rate.

Defect Complexes and Non-Equilibrium Processes Underlying the P-Type Doping of GaN

1998 ◽  
Vol 537 ◽  
Author(s):  
Fernando A. Reboredo ◽  
Sokrates T. Pantelides
Keyword(s):  
High Temperature ◽  
Experimental Evidence ◽  
First Principles ◽  
Final Anneal ◽  
First Principles Calculations ◽  
Defect Complexes ◽  
Equilibrium Processes ◽  
Open Questions ◽  
High Temperature Anneal ◽  
P Type

AbstractIt is well known that hydrogen plays a key role in p-type doping of GaN. It is believed that H passivates substitutional Mg during growth by forming a Mgs-N-Hi complex; in subsequent annealing, H is removed, resulting in p-type doping. Several open questions have remained, however, such as experimental evidence for other complexes involving Mg and H and difficulties in accounting for the relatively high-temperature anneal needed to remove H. We present first principles calculations in terms of which we show that the doping process is in fact significantly more complex. In particular, interstitial Mg plays a major role in limiting p-type doping. Overall, several substitutional/interstitial complexes form and can bind H, with vibrational frequencies that account for hitherto unidentified observed lines. We predict that these defects, which limit doping efficiency, can be eliminated by annealing in an atmosphere of H and N prior to the final anneal that removes H.

Phase Stability of the Sigma Phase in Fe-Cr Based Alloys

1995 ◽  
Vol 408 ◽  
Author(s):  
Marcel Il. F ◽  
Sluiter. Koivan Esfurjani ◽  
Yoshiyuki Kawazoe
Keyword(s):  
Total Energy ◽  
Phase Stability ◽  
First Principles ◽  
Finite Temperature ◽  
Sigma Phase ◽  
Complex Structure ◽  
Unit Cell ◽  
Energy Calculations ◽  
Cluster Variation ◽  
The Stability

AbstractThe FeCr sigma phase is a good example of a complex structure: it. has 30 atoms in the unit cell and 5 inequivalent lattice sites, and it belongs to the class of tetrahedrally close packed structures, also known as Frank-Kaspar structures. So far. such structures have riot been treated within a first-principles statistical thermodynamics framework. It will be shown that dtlme to advances in algorithms and hardware important features of the phase stability of complex phases can be computed. The factors which affect the stability of the sigma phase have been studied using carefully selected supercells for electronic total energy calculations. cluster variation calc:ulations in the tet.rahedron approximation were performed to evaluate the effect of partial disorder and of finite temperature. The preferred occupancy of the 5 lattice sites has been investigated and is compared with experimental determinations.

scholarly journals First principles study of structure, electronic and optical properties of Y3Fe5O12 in cubic and trigonal phases

2015 ◽  
Vol 33 (1) ◽  
pp. 169-174 ◽  
Author(s):  
Shen Tao ◽  
Hu Chao ◽  
Dai Hailong ◽  
Yang Wenlong ◽  
Liu Hongchen ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Energy Loss ◽  
First Principles ◽  
Structural Parameters ◽  
Band Gaps ◽  
First Principles Calculations ◽  
Electronic And Optical Properties ◽  
Direct Band ◽  
Experimental Values

AbstractFirst principles calculations have been performed to investigate the structure, electronic and optical properties of Y3Fe5O12. Both the cubic and trigonal phases have been considered in our calculation. The calculated structural parameters are slightly larger than the experimental values. The band structures show that Y3Fe5O12 in cubic and trigonal phases have direct band gaps of 0.65 and 0.17 eV. The calculations of dielectric function, absorption, extinction coefficient, refractive index, energy loss function and reflectivity are presented.

Mechanical and electronic properties of Ti-7333 alloy under tension: First-principles calculations

2020 ◽  
Vol 34 (17) ◽  
pp. 2050150
Author(s):  
Dan Hong ◽  
Wei Zeng ◽  
Fu-Sheng Liu ◽  
Bin Tang ◽  
Qi-Jun Liu
Keyword(s):  
Tensile Strength ◽  
Electronic Properties ◽  
Elastic Properties ◽  
First Principles ◽  
Structural Parameters ◽  
Tension Stress ◽  
Mechanical Parameters ◽  
First Principles Calculations ◽  
Anisotropic Behavior ◽  
Resistance To Deformation

The first-principles calculations are used to investigate the effects on mechanical and electronic properties of Ti-7333 alloy under the tension stress along [001], [100] and [110] directions. First, we study the structure and elastic properties of Ti-7333 alloy with 2, 16, 54 and 128 atoms, finding that the structural parameters of four models are comparative due to the approximate value of c/a and the elastic properties are also similar. Hence, we choose Ti-7333 alloy with 16 atoms to study the effects on mechanical and electronic properties under tension stress along [001], [100] and [110] directions. The changes of independent elastic constants, Debye temperature and anisotropic behavior under different tension stress along all the three directions can reflect that the tensile strength of Ti-7333 alloy may exist between [Formula: see text] and [Formula: see text] GPa and also find that it is easier to change the resistance to deformation of Ti-7333 alloy under the tension stress along [100] direction compared with [001] and [110] directions. What’s more, the calculated mechanical parameters show that the Ti-7333 alloy is brittle and the tendency of variations is small with the increase in tension stress. The effects on electronic properties including metallic and covalent properties are not obvious due to the approximate height of TDOS, pseudogap and charge density.

Real-space implementation of nonlocal pseudopotentials for first-principles total-energy calculations

1991 ◽  
Vol 44 (23) ◽  
pp. 13063-13066 ◽  
Author(s):  
R. D. King-Smith ◽  
M. C. Payne ◽  
J. S. Lin
Keyword(s):  
Total Energy ◽  
First Principles ◽  
Real Space ◽  
Energy Calculations
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