Study of the Non-Linearity on TiO2(0 0 1) Surface with Oxygen Defects: A First-Principles Study

NANO ◽  
2017 ◽  
Vol 12 (08) ◽  
pp. 1750097
Author(s):  
Yuehua Dai ◽  
Xu Zhang ◽  
Chengzhi Ma ◽  
Zhiyong Pan ◽  
Feifei Wang ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
First Principles ◽  
Electronic Structures ◽  
Oxygen Vacancies ◽  
Stark Effect ◽  
Energy Levels ◽  
Oxygen Interstitial ◽  
Oxygen Defects ◽  
Pseudopotential Calculations

First-principles plane-wave pseudopotential calculations were performed to study the energetics and electronic structures of oxygen defects on rutile TiO2(0 0 1). The influence of the material thickness on non-linearity (NL) was studied. With the increase in the thickness, the NL became stronger. Calculating the site-projected density of states by applying an external electric field showed that the NL of the bulk is due to the exchange of electrons between O 2p orbitals and Ti 3d orbitals. Finally, the influence of oxygen defects — oxygen vacancies (Vo), oxygen interstitials (Oi), and oxygen vacancies/oxygen interstitial (Vo[Formula: see text]Oi) pairs (Frenkel pair defects) — on the NL of TiO2 was studied. These results demonstrate that the band gap ([Formula: see text] of TiO2 became gradually narrower as the electric field increased. The Stark effect and defects can lead to the splitting of degenerate energy levels. Stronger electric fields increase the band splitting and reduce [Formula: see text]. With the increase in the Vo concentration, the decrease in the splitting amplitude and width of the energy level lead to weakening of the transfer of electrons between O and Ti atoms and optimizing the NL of TiO2. Therefore, the incorporation of Vo plays a significant role in improving the NL of TiO2.

Intersubband Transitions in Asymmetric Quantum Wells with External Electric Field

2014 ◽  
Vol 525 ◽  
pp. 170-176
Author(s):  
Zhao Xu Liu ◽  
Jun Zhu ◽  
Si Hua Ha
Keyword(s):  
Electric Field ◽  
Quantum Wells ◽  
External Electric Field ◽  
Electric Fields ◽  
Stark Effect ◽  
Energy Levels ◽  
Intersubband Transitions ◽  
External Electric Fields ◽  
Asymmetric Quantum ◽  
Negative Field

The quantum-confined Stark effect on the optical absorption of intersubband transitions in an asymmetric AlxGa1-xN/In0.3Ga0.7N/GaN quantum wells is investigated by means of the density matrix formulism. The built-in electric field generated by the piezoelectric and spontaneous polarizations competing against to the external electric fields is considered. As the result, the influences of the built-in and external electric fields on the energy potentials and the eigen stares are discussed in detail. When the positive external electric field is applied, the peak values of the absorption coefficients from 3-2, 2-1 and 3-1 transitions are reduced and moved to the lower photon energy levels. With the negative field, the exactly opposite results can be obtained. Moreover, it is indicated that the results of the wavelengths from the 3-2, 2-1 and 3-1 transitions are reduced by the positive external electric field and increased by the negative field.

Electric Field Effects on the Optical Properties of InxGa1-xAs/GaAs Strained Quantum Wells and Superlattices

1989 ◽  
Vol 160 ◽  
Author(s):  
K. Gibb ◽  
C. Lacelle ◽  
A.P. Roth ◽  
B. Soucail ◽  
N. Dupuis ◽  
...  
Keyword(s):  
Electric Field ◽  
Quantum Wells ◽  
Electric Fields ◽  
Stark Effect ◽  
Energy Levels ◽  
Precise Determination ◽  
Discrete Energy ◽  
Photocurrent Spectroscopy ◽  
Zone Centre ◽  
Photocurrent Spectra

AbstractWe have used photoluminescence excitation and photocurrent spectroscopy to investigate the electronic properties of InxGa1-xAs/GaAs strained layer quantum wells and superlattices. In quantum wells, sharp excitonic transitions between discrete energy levels are observed both in excitation and near flatband photocurrent spectra whereas superlattices show heavy-hole to conduction miniband transitions at the Brillouin mini-zone centre and edge, directly giving the electron miniband width. Applying a longitudinal electric field to the quantum wells produces a red shift of the excitons due to the quantum confined Stark effect, while in superlattices, photocurrent spectra at finite applied electric fields show for the first time in this system, the effects of Wannier-Stark quantization. The analysis of the spectra provides a precise determination of the band offset.

First-Principles Calculations of Titanium Dopants in Alumina

2005 ◽  
Vol 475-479 ◽  
pp. 3095-3098
Author(s):  
Katsuyuki Matsunaga ◽  
Teruyasu Mizoguchi ◽  
Atsutomo Nakamura ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Band Gap ◽  
First Principles ◽  
Electronic Structures ◽  
First Principles Calculations ◽  
Pseudopotential Calculations ◽  
Formation Energies

First-principles pseudopotential calculations were performed to investigate atomic and electronic structures of titanium (Ti) dopants in alumina (Al2O3). It was found that a substitutional Ti3+ defect induced an extra level occupied by one electron within the band gap of Al2O3. When two or more substitutional Ti3+ defects were located closely to each other, the defect-induced levels exhibited strong bonding interactions, and their formation energies decreased with increasing numbers of Ti3+ defects. This indicates that association and clustering of substitutional Ti3+ defects in Al2O3 can take place due to the interaction of the defect-induced levels.

The tuning effect of the electric field on the physical properties of some typical wurtzite semiconductors

2017 ◽  
Vol 31 (33) ◽  
pp. 1750310 ◽  
Author(s):  
Jia-Ning Li ◽  
San-Lue Hu ◽  
Hao-Yu Dong ◽  
Xiao-Ying Xu ◽  
Jia-Fu Wang ◽  
...  
Keyword(s):  
Electric Field ◽  
Physical Properties ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Great Influence ◽  
Semiconductor Materials ◽  
Functional Theory ◽  
The Stability ◽  
Wurtzite Semiconductors

Under the tuning of an external electric field, the variation of the geometric structures and the band gaps of the wurtzite semiconductors ZnS, ZnO, BeO, AlN, SiC and GaN have been investigated by the first-principles method based on density functional theory. The stability, density of states, band structures and the charge distribution have been analyzed under the electric field along (001) and (00[Formula: see text]) directions. Furthermore, the corresponding results have been compared without the electric field. According to our calculation, we find that the magnitude and the direction of the electric field have a great influence on the electronic structures of the wurtzite materials we mentioned above, which induce a phase transition from semiconductor to metal under a certain electric field. Therefore, we can regulate their physical properties of this type of semiconductor materials by tuning the magnitude and the direction of the electric field.

scholarly journals The stark effect of the fine-structure of hydrogen

1928 ◽  
Vol 119 (782) ◽  
pp. 313-334 ◽  
Keyword(s):  
Fine Structure ◽  
Hydrogen Atom ◽  
Electric Field ◽  
Quantum Dynamics ◽  
Stark Effect ◽  
Energy Levels ◽  
Structure Theory ◽  
Weak Electric Field ◽  
Classical Dynamics ◽  
Balmer Series

One of the earliest successes of classical quantum dynamics in a field where ordinary methods had proved inadequate was the solution, by Schwarzschild and Epstein, of the problem of the hydrogen atom in an electric field. It was shown by them that under the influence of the electric field each of the energy levels in which the unperturbed atom can exist on Bohr’s original theory breaks up into a number of equidistant levels whose separation is proportional to the strength of the field. Consequently, each of the Balmer lines splits into a number of components with separations which are integral multiples of the smallest separation. The substitution of the dynamics of special relativity for classical dynamics in the problem of the unperturbed hydrogen atom led Sommerfeld to his well-known theory of the fine-structure of the levels; thus, in the absence of external fields, the state n = 1 ( n = 2 in the old notation) is found to consist of two levels very close together, and n = 2 of three, so that the line H α of the Balmer series, which arises from a transition between these states, has six fine-structure components, of which three, however, are found to have zero intensity. The theory of the Stark effect given by Schwarzschild and Epstein is adequate provided that the electric separation is so much larger than the fine-structure separation of the unperturbed levels that the latter may be regarded as single; but in weak fields, when this is no longer so, a supplementary investigation becomes necessary. This was carried out by Kramers, who showed, on the basis of Sommerfeld’s original fine-structure theory, that the first effect of a weak electric field is to split each fine-structure level into several, the separation being in all cases proportional to the square of the field so long as this is small. When the field is so large that the fine-structure is negligible in comparison with the electric separation, the latter becomes proportional to the first power of the field, in agreement with Schwarzschild and Epstein. The behaviour of a line arising from a transition between two quantum states will be similar; each of the fine-structure components will first be split into several, with a separation proportional to the square of the field; as the field increases the separations increase, and the components begin to perturb each other in a way which leads ultimately to the ordinary Stark effect.

scholarly journals Supramolecular Stark Effect in Host-Guest Complexes via Charge Density Analysis

2014 ◽  
Vol 70 (a1) ◽  
pp. C674-C674
Author(s):  
Sajesh Thomas ◽  
Rebecca Fuller ◽  
Alexandre Sobolev ◽  
Philip Schauer ◽  
Simon Grabowsky ◽  
...  
Keyword(s):  
Electric Field ◽  
Charge Density ◽  
Electric Fields ◽  
Active Sites ◽  
Stark Effect ◽  
Dipole Moments ◽  
Covalent Bonds ◽  
Guest Molecules ◽  
Density Mapping ◽  
Density Analysis

The effect of an electric field on the vibrational spectra, the Vibrational Stark Effect (VSE), has been utilized extensively to probe the local electric field in the active sites of enzymes [1, 2]. For this reason, the electric field and consequent polarization effects induced by a supramolecular host system upon its guest molecules attain special interest due to the implications for various biological processes. Although the host-guest chemistry of crown ether complexes and clathrates is of fundamental importance in supramolecular chemistry, many of these multicomponent systems have yet to be explored in detail using modern techniques [3]. In this direction, the electrostatic features associated with the host-guest interactions in the inclusion complexes of halogenated acetonitriles and formamide with 18-crown-6 host molecules have been analyzed in terms of their experimental charge density distribution. The charge density models provide estimates of the molecular dipole moment enhancements which correlate with the simulated values of dipole moments under electric field. The accurate electron density mapping using the multipole formalism also enable the estimation of the electric field experienced by the guest molecules. The electric field vectors thus obtained were utilized to estimate the vibrational stark effect in the nitrile (-C≡N) and carbonyl (C=O) stretching frequencies of the guest molecules via quantum chemical calculations in gas phase. The results of these calculations indicate remarkable elongation of C≡N and C=O bonds due to the electric fields. The electronic polarization in these covalent bonds induced by the field manifests as notable red shifts in their characteristic vibrational frequencies. These results derived from the charge densities are further supported by FT-IR experiments and thus establish the significance of a phenomenon that could be termed as the "supramolecular Stark effect" in crystal environment.

POLARIZABILITY AND SHIELDING OF COAXIAL HYBRID DOUBLE-WALLED NANOTUBES: A FIRST-PRINCIPLES STUDY

2008 ◽  
Vol 07 (04) ◽  
pp. 793-803
Author(s):  
NUANXIANG LI ◽  
QUNXIANG LI ◽  
HAIBIN SU ◽  
Q. W. SHI ◽  
JINLONG YANG
Keyword(s):  
Carbon Nanotube ◽  
Boron Nitride ◽  
Electric Field ◽  
Electronic Properties ◽  
External Electric Field ◽  
First Principles ◽  
Electronic Structures ◽  
Outer Tube ◽  
Boron Nitride Nanotube ◽  
First Principles Study

First-principles studies on electronic structures, transverse polarizability, and shielding of two coaxial hybrid double-walled nanotubes consisting of carbon nanotube (CNT) and boron nitride nanotube (BNNT), namely CNT@BNNT and BNNT@CNT, are conducted. The interaction between inner and outer tubes is considerably weak. The polarizability of single-walled CNT is larger than that of single-walled BNNT due to the different electronic properties. In BNNT@CNT, the outer CNT with delocalized π-electrons character demonstrates a nearly complete shielding with the order of 90% of the inner BNNT from the transverse external electric field, while the outer BNNT has a relative small shielding of about 40% for the inner CNT in CNT@BNNT system. Moreover, the shielding of the outer tube can be appreciably enhanced by increasing the intertube separation.

scholarly journals A Preorganized Electric Field Leads to Minimal Geometrical Reorientation in the Catalytic Reaction of Ketosteroid Isomerase

2020 ◽  
Author(s):  
Yufan Wu ◽  
Stephen Fried ◽  
Steven Boxer
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ground State ◽  
Active Site ◽  
Electrostatic Interactions ◽  
Stark Effect ◽  
Structural Changes ◽  
Enzymatic Catalysis ◽  
Ketosteroid Isomerase ◽  
Computational Enzyme Design

<div><p>Electrostatic interactions play a pivotal role in enzymatic catalysis and are increasingly modeled explicitly in computational enzyme design; nevertheless, they are challenging to measure experimentally. Using vibrational Stark effect (VSE) spectroscopy, we have measured electric fields inside the active site of the enzyme ketosteroid isomerase (KSI). These studies have shown that these fields can be unusually large, but it has been unclear to what extent they specifically stabilize the transition state (TS) relative to a ground state (GS). In the following, we use crystallography and computational modeling to show that KSI’s intrinsic electric field is nearly perfectly oriented to stabilize the geometry of its reaction’s TS. Moreover, we find that this electric field adjusts the orientation of its substrate in the ground state so that the substrate needs to only undergo minimal structural changes upon activation to its TS. This work provides evidence that the active site electric field in KSI is preorganized to facilitate catalysis and provides a template for how electrostatic preorganization can be measured in enzymatic systems. <br></p></div>

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