Ab initiostudies of electronic structure of defects on the Te sites in PbTe

2005 ◽  
Vol 886 ◽  
Author(s):  
Salameh Ahmad ◽  
S. D. Mahanti ◽  
M. G. Kanatzidis
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Ternary Systems ◽  
Electronic Structure Calculations ◽  
Valence Band Maximum ◽  
Defect States ◽  
Electronic Density ◽  
Substitutional Defect ◽  
New States ◽  
Structure Calculations

ABSTRACTAb initioelectronic structure calculations have been carried out to understand the nature of anionic defect states in PbTe. We find that Te vacancies strongly perturb the electronic density of states (DOS) near the band gap region. New states of predominantly Pb p character appear in the band gap. Iodine is an ideal substitutional defect and a donor. Sulpher and Selenium do not affect the states near the conduction band minimum but suppress the DOS near the valence band maximum. These results have important implications on the thermoelectric properties of PbTe and PbTexM1−x(M=S, Se) ternary systems.

Electronic Structure of Defects in SnTe

2013 ◽  
Vol 701 ◽  
pp. 125-130
Author(s):  
Salameh Ahmad
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Valence Band ◽  
Fundamental Difference ◽  
Density Of State ◽  
Defect States ◽  
Deep Defect ◽  
Conduction Bands ◽  
Resonant States ◽  
Structure Calculations

Myab initioelectronic structure calculations inRSn2n-1Te2n, n=16, R = a vacancy, Cd, and In show that when Sn atom is substituted by R, the Density of State (DOS) of the valence and conduction bands get strongly perturbed. There are significant changes near the band gap region. Sn vacancy causes very little change near the bottom of the conduction band DOS whereas there is an increase in the DOS near the top of the valence band. Results for In impurity shows that, unlike PbTe, the deep defect states in SnTe are resonant states near the top of the valence band. In PbTe these deep defect states lie in the band-gap region (act asn-type). This fundamental difference in the position of the deep defect states in SnTe and PbTe explains the experimental anomalies seen in the case of In impurities (act asn-type in PbTe andp-type in SnTe).

Native Defect Formation and Ionization Energies in Cadmium Telluride

2002 ◽  
Vol 719 ◽  
Author(s):  
John E. Jaffe ◽  
Mary Bliss
Keyword(s):  
Defect Formation ◽  
Energy Levels ◽  
Lattice Relaxation ◽  
Electronic Structure Calculations ◽  
Valence Band Maximum ◽  
Native Defect ◽  
Defect States ◽  
Donor States ◽  
Structure Calculations ◽  
Intrinsic Energy

AbstractDeep intrinsic energy levels near the middle of the band gap in CdTe have been reported in a number of experiments. Based on earlier defect-supercell electronic structure calculations, at least some of these features have been attributed to the second ionization level of the Cd vacancy, while the TeCd antisite, possibly complexed with a Cd vacancy, has also been suggested to account for some midgap levels. Using high-accuracy LDA calculations with full lattice relaxation out to third neighbors, we find that (i) both acceptor states of the Cd vacancy are shallow, (ii) the donor states of an isolated TeCd are both more than 1 eV above the valence band maximum, (iii) the TeCd-VCd complex does indeed have acceptor states near midgap in CdTe and probably accounts for the native defect states in that energy range.

New Thermoelectric Arsenides and Antimonides for High Temperature Applications

2007 ◽  
Vol 1044 ◽  
Author(s):  
Hong Xu ◽  
Navid Soheilnia ◽  
Huqin Zhang ◽  
Paola N. Alboni ◽  
Terry M. Tritt ◽  
...  
Keyword(s):  
Electronic Structure ◽  
High Temperature ◽  
Transition Metal ◽  
Band Gap ◽  
Electronic Structure Calculations ◽  
Metal Atoms ◽  
Transition Metal Atoms ◽  
Valence Electrons ◽  
Type Semiconductor ◽  
Structure Calculations

AbstractThree different materials crystallizing in the cubic Ir3Ge7 type are under investigation in our group, namely Mo3(Sb,Te)7, Nb3(Sb,Te)7, and Re3(E,As)7 (with E = Si, Ge, Sn). Our electronic structure calculations reveal a band gap to occur at 55 valence-electrons in all three cases, namely Mo3Sb5Te2, Nb3Sb2Te5, and Re3EAs6. Cubic holes exist in these structures that may be filled with small cations such as 3d transition metal atoms. Ni0.06Mo3Sb5.4Te1.6 is a degenerate p-type semiconductor that reaches ZT = 0.96 at 750°C, while Re3Ge0.6As6.4 is a degenerate n- type semiconductor with slightly lower ZT values. Preliminary results indicate that the Re3(Sn,As)7 system may be the most promising of the rhenium arsenides.

scholarly journals Electronic Structure Calculations of Calcium Silicate Hydrates

1995 ◽  
Vol 412 ◽  
Author(s):  
P. A. Sterne ◽  
A. Meike
Keyword(s):  
Electronic Structure ◽  
Chemical Reactions ◽  
Calcium Silicate ◽  
Electronic Structure Calculations ◽  
Lattice Parameters ◽  
Electronic Density ◽  
Calcium Silicate Hydrates ◽  
State Densities ◽  
Structure Calculations ◽  
Good Agreement

AbstractMany phases in the calcium-silicate-hydrate system can develop in cement exposed over long periods of time to temperatures above 25°C. As a consequence, chemical reactions involving these phases can affect the relative humidity and water chemistry of a radioactive waste repository that contains significant amounts of cement. In order to predict and simulate these chemical reactions, we are developing an internally consistent database of crystalline Ca-Si-hydrate structures. The results of first principles electronic structure calculations on two such phases, wollastonite (CaSiO3) and xonotlite (Ca6Si6O17(OH)2), are reported here. The calculated ground state properties are in very good agreement with experiment, providing equilibrium lattice parameters within about 1–1.4% of the experimentally reported values. The roles of the different types of oxygen atoms, which are fundamental to understanding the energetics of crystalline Ca-Si-hydrates are briefly discussed in terms of their electronic state densities. The good agreement with experiment for the lattice parameters and the consistency of the electronic density of states features for the two structures demonstrate the applicability of these electronic structure methods in calculating the fundamental properties of these phases.

Message Passing Neural Networks for Partial Charge Assignment to Metal-Organic Frameworks

2020 ◽  
Author(s):  
Ali Raza ◽  
Arni Sturluson ◽  
Cory Simon ◽  
Xiaoli Fern
Keyword(s):  
Electronic Structure ◽  
Message Passing ◽  
Gas Adsorption ◽  
Metal Organic Frameworks ◽  
Computational Cost ◽  
Electronic Structure Calculations ◽  
High Fidelity ◽  
Partial Charges ◽  
Metal Organic ◽  
Structure Calculations

Virtual screenings can accelerate and reduce the cost of discovering metal-organic frameworks (MOFs) for their applications in gas storage, separation, and sensing. In molecular simulations of gas adsorption/diffusion in MOFs, the adsorbate-MOF electrostatic interaction is typically modeled by placing partial point charges on the atoms of the MOF. For the virtual screening of large libraries of MOFs, it is critical to develop computationally inexpensive methods to assign atomic partial charges to MOFs that accurately reproduce the electrostatic potential in their pores. Herein, we design and train a message passing neural network (MPNN) to predict the atomic partial charges on MOFs under a charge neutral constraint. A set of ca. 2,250 MOFs labeled with high-fidelity partial charges, derived from periodic electronic structure calculations, serves as training examples. In an end-to-end manner, from charge-labeled crystal graphs representing MOFs, our MPNN machine-learns features of the local bonding environments of the atoms and learns to predict partial atomic charges from these features. Our trained MPNN assigns high-fidelity partial point charges to MOFs with orders of magnitude lower computational cost than electronic structure calculations. To enhance the accuracy of virtual screenings of large libraries of MOFs for their adsorption-based applications, we make our trained MPNN model and MPNN-charge-assigned computation-ready, experimental MOF structures publicly available.<br>

scholarly journals Quantum HF/DFT-embedding algorithms for electronic structure calculations: Scaling up to complex molecular systems

2021 ◽  
Vol 154 (11) ◽  
pp. 114105
Author(s):  
Max Rossmannek ◽  
Panagiotis Kl. Barkoutsos ◽  
Pauline J. Ollitrault ◽  
Ivano Tavernelli
Keyword(s):  
Electronic Structure ◽  
Electronic Structure Calculations ◽  
Scaling Up ◽  
Molecular Systems ◽  
Structure Calculations

scholarly journals Scaling up electronic structure calculations on quantum computers: The frozen natural orbital based method of increments

2021 ◽  
Vol 155 (3) ◽  
pp. 034110
Author(s):  
Prakash Verma ◽  
Lee Huntington ◽  
Marc P. Coons ◽  
Yukio Kawashima ◽  
Takeshi Yamazaki ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Electronic Structure Calculations ◽  
Scaling Up ◽  
Quantum Computers ◽  
Natural Orbital ◽  
Structure Calculations
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