Jacob Gavartin - Academia.edu (original) (raw)

Papers by Jacob Gavartin

arXiv: Quantum Physics, 2020

Numerous reports claim that quantum advantage, which should emerge as a direct consequence of the... more Numerous reports claim that quantum advantage, which should emerge as a direct consequence of the advent of quantum computers, will herald a new era of chemical research because it will enable scientists to perform the kinds of quantum chemical simulations that have not been possible before. Such simulations on quantum computers, promising a significantly greater accuracy and speed, are projected to exert a great impact on the way we can probe reality, predict the outcomes of chemical experiments, and even drive design of drugs, catalysts, and materials. In this work we review the current status of quantum hardware and algorithm theory and examine whether such popular claims about quantum advantage are really going to be transformative. We go over subtle complications of quantum chemical research that tend to be overlooked in discussions involving quantum computers. We estimate quantum computer resources that will be required for performing calculations on quantum computers with che...

Organic Light Emitting Materials and Devices XX, 2016

Using periodic plane wave DFT and embedded cluster methods we have studied the structure and elec... more Using periodic plane wave DFT and embedded cluster methods we have studied the structure and electronic properties of neutral and charged O, N and H defects in prototype gate oxides: monoclinic ZrO2 and HfO2. The structure, ionisation energies and electron affinities of oxygen vacancies, interstitial oxygen and nitrogen atoms and molecules in different charge states were calculated. The positions of

Microelectronic Engineering, 2007

We predict, by means of ab initio calculations, the existence of electron and hole polaron states... more We predict, by means of ab initio calculations, the existence of electron and hole polaron states in m-HfO 2 . Holes were found to self-trap on 3-and 4-coordinated oxygen ions while electron polaron is localized over three neighboring Hf atoms. We calculated the self-trapping energies, diffusion barriers, ionization energies and ESR g-tensors characterizing these polaron states. Both types of polarons have very small hopping diffusion barriers, less than 0.1 eV, and should be mobile at low temperatures.

Journal of Physics Condensed Matter, Nov 15, 2001

Utilizing the harmonic approximation, we introduce a simple technique for the generation of ensem... more Utilizing the harmonic approximation, we introduce a simple technique for the generation of ensembles of thermally disordered atomic structures, and calculate for the MgO crystal electron densities of states (DOS) and the on-site potential probability distributions for the ensembles generated within the classical and quasi-classical harmonic approximations, molecular dynamics and uncorrelated Gaussian atomic disorder models. An account of the zero-energy vibrations even at room temperature results in a significant increase in the mean square atomic displacements and, thus, in the probability distributions of the electrostatic potential and ultimately in the extent of the band tails in the electron DOS. We also demonstrate that the correlations in atomic positions affect the electronic structure. We have evaluated directly the on-site potential autocorrelation function (PAF) for all disorder models, as well as the temperature dependence of the PAF. The correlation length, L, is shown to be less than the second nearest neighbour at low temperature and decreasing to below the nearest neighbour distance at T = 500 K. The short correlation length obtained in the direct modelling is in agreement with the Urbach-Martienssen rule for the optical absorption edge observed experimentally.

Physical Review B Condensed Matter and Materials Physics, 2007

ABSTRACT

Journal of the Korean Ceramic Society, 2016

Continued miniaturization and increasingly exact requirements for thin film deposition in the sem... more Continued miniaturization and increasingly exact requirements for thin film deposition in the semiconductor industry is driving the search for new effective, efficient, selective precursors and processes. The requirements of defect-free, conformal films, and precise thickness control have focused attention on atomic layer deposition (ALD). ALD precursors so far have been developed through a trial-and-error experimental approach, leveraging the expertise and tribal knowledge of individual research groups. Precursors can show significant variation in performance, depending on specific choice of co-reactant, deposition stage, and processing conditions. The chemical design space for reactive thin film precursors is enormous and there is urgent need for the development of computational approaches to help identify new ligand-metal architectures and functional co-reactants that deliver the required surface activity for next-generation thin-film deposition processes. In this paper we discuss quantum mechanical simulation (e.g. density functional theory, DFT) applied to ALD precursor reactivity and state-of-the-art automated screening approaches to assist experimental efforts leading toward optimized precursors for next-generation ALD processes.

Materials Science and Engineering C, 2007

ABSTRACT However fascinating structures may be at the nanoscale, time-dependent behaviour at the ... more ABSTRACT However fascinating structures may be at the nanoscale, time-dependent behaviour at the nanoscale has far greater importance. Some of the dynamics is random, with fluctuations controlling rate processes and making thermal ratchets possible. Some of the dynamics causes the transfer of energy, of signals, or of charge. Such transfers are especially efficiently controlled in biological systems. Other dynamical processes occur when we wish to control the nanoscale, e.g., to avoid local failures of gate dielectrics, or to manipulate structures by electronic excitation, to use spin manipulation in quantum information processing. Our prime purpose is to make clear the enormous range and variety of time-dependent nanoscale phenomena.

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences

Hafnium dioxide currently is considered a dielectric of choice for novel MOSFET devices but it ha... more Hafnium dioxide currently is considered a dielectric of choice for novel MOSFET devices but it has an important drawback (as most high-k films on silicon) of low crystallization temperature. We use large scale plane wave density functional simulations of the HfO2/SiOx/Si system to determine the properties of the amorphous hafnia films and the mechanisms of their crystallization and defects formation

2006 International Symposium on VLSI Technology, Systems, and Applications, 2006

The results in this paper suggest that migration of the electrons, captured during the fast charg... more The results in this paper suggest that migration of the electrons, captured during the fast charging process, to other available traps represents the major process responsible for the intrinsic Vt instability in the high-k NMOS transistors. The extracted trap characteristics are consistent with those of the oxygen vacancies in the monoclinic hafnia

NATO Science Series II: Mathematics, Physics and Chemistry, 2006

Properties of the defects responsible for fast transient electron trapping phenomenon in high-k g... more Properties of the defects responsible for fast transient electron trapping phenomenon in high-k gate dielectrics were investigated. It was shown that electrons might be reversibly trapped at shallow, delocalized gap states. Ab initio calculations have indicated that Zr substitutional impurities and fourcoordinated negatively charged O vacancies can fit the electrical profile of the electron traps. The relationship between trap characteristics

Physica B: Condensed Matter, 2002

We use the Mott-Littleton approach to evaluate the electronic and ionic polarisation energies in ... more We use the Mott-Littleton approach to evaluate the electronic and ionic polarisation energies in LaMnO 3 lattice associated with holes localised on both Mn 3þ cation and O 2À anion. The full lattice relaxation energy for a hole localised at the O-site is estimated as 2:4 eV which is appreciably greater than that of 0:8 eV for a hole localised at the Mn-site, indicating the strong electron-phonon interaction in the former case. The calculated thermal energies of the hole formation predict that the electronic hole is marginally more stable in the Mn 4þ state in LaMnO 3 host lattice, but the energy of a hole in the O À state is only higher by a small amount, rather suggesting that both possibilities should be treated seriously. r

MRS Proceedings, 1995

ABSTRACTThe changes in the radial distribution function (RDF) and vibrational density of states (... more ABSTRACTThe changes in the radial distribution function (RDF) and vibrational density of states (DOS) of porous silicon (p-Si) with change of porosity are studied within a modified diffusion limited aggregation model and molecular dynamics simulations. By decomposing the first peak of the radial distribution function of p-Si on to partial RDFs, for atoms having different coordinations, and partial RDFs, for bonds connecting atoms with different coordinations, we show that appearance of the structure in the first peak of the RDF in p-Si is stipulated by bonds between undercoordinated surface atoms. The vibrational DOS projected on surface atoms are also shown to be different from that corresponding to crystalline phonons. It is characterised by the relative increase of the intensity of vibrations in the acoustic region and by appearance of surface-like vibrations split from the optical band.

MRS Proceedings, 1997

We apply the frozen phonon and molecular dynamics methods within the semiempirical orthogonal tig... more We apply the frozen phonon and molecular dynamics methods within the semiempirical orthogonal tight-binding framework to study the anomalous behaviour of the (0001) optical longitudinal (LO) and transverse (TO) phonons in the low temperature hep phase of Ti, and the ⅔[111]L and ½[110]T1 phonons in the high temperature bec phase. We demonstrate that, in agreement with previous findings in Zr, the anomalous thermal frequency shifts in hep Ti are related to the strong coupling of the electron density of states (DOS) to the particular lattice distortions. The distortions along the bec ⅔[111]L and ½[110]T1 phonons also significantly affect the DOS, resulting in the instability of these modes at low temperatures and triggering the bcc-hep and bcc-ω phase transformations.

Physical Review B, 2003

We discuss the adiabatic self-trapping of small polarons within the density functional theory (DF... more We discuss the adiabatic self-trapping of small polarons within the density functional theory (DFT). In particular, we carried out plane-wave pseudo-potential calculations of the triplet exciton in NaCl and found no energy minimum corresponding to the self-trapped exciton (STE) contrary to the experimental evidence and previous calculations. To explore the origin of this problem we modelled the self-trapped hole in NaCl using hybrid density functionals and an embedded cluster method. Calculations show that the stability of the self-trapped state of the hole drastically depends on the amount of the exact exchange in the density functional: at less than 30% of the Hartree-Fock exchange, only delocalized hole is stable, at 50% -both delocalized and self-trapped states are stable, while further increase of exact exchange results in only the self-trapped state being stable. We argue that the main contributions to the self-trapping energy such as the kinetic energy of the localizing charge, the chemical bond formation of the di-halogen quasi molecule, and the lattice polarization, are represented incorrectly within the Kohn-Sham (KS) based approaches.

Physical Review B, 2001

... of an ensemble of atomic configurations within one Hamiltonian and the subsequent analysis of... more ... of an ensemble of atomic configurations within one Hamiltonian and the subsequent analysis of the ... On the other hand, the effective charges obtained in the quantum-chemical calculations for the perfect ... As we discuss below, this may not be a general feature, but at this point it ...

Physical chemistry chemical physics : PCCP, Jan 7, 2006

We use plane wave and embedded cluster ab initio density functional calculations to study adsorpt... more We use plane wave and embedded cluster ab initio density functional calculations to study adsorption, dissociation and diffusion of the HCl molecule on the MgO(001) surface. The two methods yield comparable results for adsorption of an isolated HCl molecule and complement each other when considering charged species and coverage effects. We find dissociative chemisorption at a coverage smaller than 0.5 monolayer with a Cl(-) ion electrostatically coupled to the OH(-) ion at the surface oxygen site. The adsorption energy of the Cl(-)[dot dot dot](OH)(-) complex is 1.5 eV and the activation energy of Cl(-) diffusion away from OH(-) is 0.6 eV. There is no significant activation energy for rotation of Cl(-) around the adsorption site. At rising coverage, an increase in dipole-dipole repulsion between HCl molecules leads to a lowering of the adsorption energy per HCl and a change of binding towards hydrogen-bridge type as well as a lowering of the activation energy for Cl(-) diffusion. OH...

Nano and Giga Challenges in Microelectronics, 2003