Imperial College London

ProfessorDimitriVvedensky

Faculty of Natural SciencesDepartment of Physics

Professor of Physics
 
 
 
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Contact

 

+44 (0)20 7594 7605d.vvedensky Website

 
 
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Assistant

 

Mrs Carolyn Dale +44 (0)20 7594 7579

 
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Location

 

813Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

239 results found

Meine DCA, Vvedensky DD, 2023, Emergence of speculation in a hierarchical agent-based model, PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 620, ISSN: 0378-4371

Journal article

Bhatnagar A, Vvedensky DD, 2022, Quantum effects in an expanded Black-Scholes model, EUROPEAN PHYSICAL JOURNAL B, Vol: 95, ISSN: 1434-6028

Journal article

Capuozzo P, Panella E, Gherardini TS, Vvedensky DDet al., 2021, Path integral Monte Carlo method for option pricing, PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 581, ISSN: 0378-4371

Journal article

Mittal S, Westbroek MJE, King PR, Vvedensky DDet al., 2020, Path integral Monte Carlo method for the quantum anharmonic oscillator, EUROPEAN JOURNAL OF PHYSICS, Vol: 41, ISSN: 0143-0807

Journal article

Gocalinska AM, Mura EE, Manganaro M, Juska G, Dimastrodonato V, Thomas K, Zangwill A, Vvedensky DD, Pelucchi Eet al., 2020, Early stages of InP nanostructure formation on AlInAs, PHYSICAL REVIEW B, Vol: 101, ISSN: 2469-9950

Journal article

Westbroek MJE, Coche G-A, King PR, Vvedensky DDet al., 2019, Pressure statistics from the path integral for Darcy flow through random porous media, Journal of Physics A: Mathematical and Theoretical, Vol: 52, ISSN: 1751-8113

The path integral for classical statistical dynamics is used to determine the properties of one-dimensional Darcy flow through a porous medium with a correlated stochastic permeability for several spatial correlation lengths. Pressure statistics are obtained from the numerical evaluation of the path integral by using the Markov chain Monte Carlo method. Comparisons between these pressure distributions and those calculated from the classic finite-volume method for the corresponding stochastic differential equation show excellent agreement for Dirichlet and Neumann boundary conditions. The evaluation of the variance of the pressure based on a continuum description of the medium provides an estimate of the effects of discretization. Log-normal and Gaussian fits to the pressure distributions as a function of position within the porous medium are discussed in relation to the spatial extent of the correlations of the permeability fluctuations.

Journal article

Westbroek MJE, King PR, Vvedensky DD, Schwede RLet al., 2019, Pressure and flow statistics of Darcy flow from simulated annealing, Publisher: arXiv

The pressure and flow statistics of Darcy flow through a random permeablemedium are expressed in a form suitable for evaluation by the method ofsimulated annealing. There are several attractive aspects to using simulatedannealing: (i) any probability distribution can be used for the permeability,(ii) there is no need to invert the transmissibility matrix which, while not afactor for single-phase flow, offers distinct advantages for the case ofmultiphase flow, and (iii) the action used for simulated annealing is eminentlysuitable for coarse graining by integrating over the short-wavelength degreesof freedom. In this paper, we show that the pressure and flow statisticsobtained by simulated annealing are in excellent agreement with the moreconventional finite-volume calculations.

Working paper

Posthuma de Boer J, Ford IJ, Kantorovich L, Vvedensky DDet al., 2018, Phase-field method for epitaxial kinetics on surfaces, Journal of Chemical Physics, Vol: 149, ISSN: 0021-9606

We present a procedure for simulating epitaxial growth based on the phase-field method. We consider a basic model in which growth is initiated by a flux of atoms onto a heated surface. The deposited atoms diffuse in the presence of this flux and eventually collide to form islands which grow and decay by the attachment and detachment of migrating atoms at their edges. Our implementation of the phase-field method for this model includes uniform deposition, isotropic surface diffusion, and stochastic nucleation (in both space and time), which creates islands whose boundaries evolve as the surface atoms "condense" into and "evaporate" from the islands. Computations using this model in the submonolayer regime, prior to any appreciable coalescence of islands, agree with the results of kinetic Monte Carlo (KMC) simulations for the coverage-dependence of adatom and island densities and island-size distributions, for both reversible and irreversible growth. The scaling of the island density, as obtained from homogeneous rate equations, agrees with KMC simulations for irreversible growth and for reversible growth for varying deposition flux at constant temperature. For reversible growth with varying temperature but constant flux, agreement relies on an estimate of the formation energy of the critical cluster. Taken together, our results provide a comprehensive analysis of the phase-field method in the submonolayer regime of epitaxial growth, including the verification of the main scaling laws for adatoms and island densities and the scaling functions for island-size distributions, and point to the areas where the method can be extended and improved.

Journal article

Nasrollahi H, Vvedensky DD, 2018, Local normal modes and lattice dynamics, Journal of Applied Physics, Vol: 124, ISSN: 0021-8979

The calculation of phonon dispersion for crystalline solids with r atoms in a unit cell requires solving a 3r-dimensional eigenvalue problem. We propose a simplified approach to lattice dynamics which yields approximate analytical expressions and accurate numerical solutions to phonon dispersion without explicitly solving this eigenvalue problem. This is accomplished by a coordinate transformation to the normal modes of the isolated primitive unit cell, which is extended over the entire crystal by Fourier transformation, so each phonon branch is labelled by the irreducible representations of the symmetry group of the unit cell from which the atomic displacements can be readily identified from standard group theoretic methods. The resulting dynamical matrix is analyzed perturbatively, with the diagonal elements as the zeroth-order matrix and the off-diagonal elements as the perturbation. The zeroth-order matrix provides approximate analytical expressions for the phonon dispersions, the first-order terms vanish, with the higher-order terms converging to the exact solutions. We describe the application of this method to a one-dimensional diatomic chain, graphene, and hexagonal close-packed zirconium. In all cases, the zeroth-order solution provides reasonable approximations, while the second-order solutions already show the rapid convergence to the exact dispersion curves. This methodology provides insight into the lattice dynamics of crystals, molecular solids, and Jahn--Teller systems, while significantly reducing the computational cost. Similarities between our method and other techniques that use local basis sets for calculating electronic and vibrational properties of materials are discussed. We conclude by exploring extensions that widen the scope of our approach.

Journal article

Westbroek MJE, Coche G-A, King PR, Vvedensky DDet al., 2018, Evaluation of the path integral for flow through random porous media, Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 97, Pages: 1-5, ISSN: 1539-3755

We present a path integral formulation of Darcy's equation in one dimension with random permeability described by a correlated multivariate lognormal distribution. This path integral is evaluated with the Markov chain Monte Carlo method to obtain pressure distributions, which are shown to agree with the solutions of the corresponding stochastic differential equation for Dirichlet and Neumann boundary conditions. The extension of our approach to flow through random media in two and three dimensions is discussed.

Journal article

Westbroek MJE, King PR, Vvedensky DD, Dürr Set al., 2018, User's guide to Monte Carlo methods for evaluating path integrals, American Journal of Physics, Vol: 86, Pages: 293-304, ISSN: 0002-9505

We give an introduction to the calculation of path integrals on a lattice, with the quantum harmonic oscillator as an example. In addition to providing an explicit computational setup and corresponding pseudocode, we pay particular attention to the existence of autocorrelations and the calculation of reliable errors. The over-relaxation technique is presented as a way to counter strong autocorrelations. The simulation methods can be extended to compute observables for path integrals in other settings.

Journal article

Pelucchi E, Moroni ST, Dimastrodonato V, Vvedensky DDet al., 2018, Self-ordered nanostructures on patterned substrates: experiment and theory of metalorganic vapor-phase epitaxy of V-groove quantum wires and pyramidal quantum dots, Journal of Materials Science: Materials in Electronics, Vol: 29, Pages: 952-967, ISSN: 0957-4522

The formation of nanostructures during metalorganic vapor-phase epitaxy on patterned (001)/(111)B GaAs substrates is reviewed. The focus of this review is on the seminal experiments that revealed the key kinetic processes during nanostructure formation and the theory and modelling that explained the phenomenology in successively greater detail. Experiments have demonstrated that V-groove quantum wires and pyramidal quantum dots result from self-limiting concentration profiles that develop at the bottom of V-grooves and inverted pyramids, respectively. In the 1950s, long before the practical importance of patterned substrates became evident, the mechanisms of capillarity during the equilibration of non-planar surfaces were identified and characterized. This was followed, from the late 1980s, by the identification of growth rate anisotropies (i.e. differential growth rates of crystallographic facets) and precursor decomposition anisotropies, with parallel developments in the fabrication of V-groove quantum wires and pyramidal quantum dots. The modelling of these growth processes began at the scale of facets and culminated in systems of coupled reaction–diffusion equations, one for each crystallographic facet that defines the pattern, which takes account of the decomposition and surface diffusion kinetics of the group-III precursors and the subsequent surface diffusion and incorporation of the group-III atoms released by these precursors. Solutions of the equations with optimized parameters produced concentration profiles that provided a quantitative interpretation of the time-, temperature-, and alloy-concentration-dependence of the self-ordering process seen in experiments.

Journal article

Leonard AS, Lee J, Schubert D, Croen LA, Fallin MD, Newschaffer CJ, Walker CK, Salafia CM, Morgan SP, Vvedensky DDet al., 2017, Scaling of the surface vasculature on the human placenta, Physical Review E, Vol: 96, ISSN: 1539-3755

The networks of veins and arteries on the chorionic plate of the human placenta are analyzed in terms of Voronoi cells derived from these networks. Two groups of placentas from the United States are studied: a population cohort with no prescreening, and a cohort from newborns with an elevated risk of developing autistic spectrum disorder. Scaled distributions of the Voronoi cell areas in the two cohorts collapse onto a single distribution, indicating common mechanisms for the formation of the complete vasculatures, but which have different levels of activity in the two cohorts.

Journal article

Vvedensky DD, 2017, Symmetry and Spectroscopy, ENCYCLOPEDIA OF SPECTROSCOPY AND SPECTROMETRY, 3RD EDITION, VOL 4: S-Z, Editors: Lindon, Tranter, Koppenaal, Publisher: ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD, Pages: 396-400

Book chapter

Nasrollahi, Vvedensky DD, 2016, Cooperative Jahn–Teller phase transition of icosahedral molecular units, Journal of Physics - Condensed Matter, Vol: 29, ISSN: 0953-8984

Non-linear molecules undergo distortions when the orbital degeneracy of the highest occupied level is lifted by the Jahn–Teller effect. If such molecules or clusters of atoms are coupled to one another, the system may experience a cooperative Jahn–Teller effect (CJTE). In this paper, we describe a model of how the CJTE leads to the crystallization of the disordered phase. The model Hamiltonian is based on a normal mode decomposition of the clusters in order to maintain the symmetry labels. We take account of the electron-strain and the electron-phonon couplings and, by displacing the coordinates of the oscillators, obtain a term that explicitly couples the Jahn–Teller centers, enabling us to perform a mean-field analysis. The calculation of the free energy then becomes straightforward, and obtaining phase diagrams in various regimes follows from the minimization of this free energy. The results show that the character of the phase transition may change from strong to weak first order and even to second-order, depending on the coupling to the vibrational modes. Taken together, these results may serve as a paradigm for crystallization near the transition temperature, where the atoms tend to form clusters of icosahedral symmetry.

Journal article

Tetlow H, Posthuma de Boer J, Ford IJ, Vvedensky DD, Curcio D, Omiciuolo L, Lizzit S, Baraldi A, Kantorovich Let al., 2016, Ethylene decomposition on Ir(111): initial path to graphene formation., Physical Chemistry Chemical Physics, Vol: 18, Pages: 27897-27909, ISSN: 1463-9084

The complete mechanism behind the thermal decomposition of ethylene (C2H4) on Ir(111), which is the first step of graphene growth, is established for the first time employing a combination of experimental and theoretical methods. High-resolution X-ray photoelectron spectroscopy was employed, along with calculations of core level binding-energies, to identify the surface species and their evolution as the surface temperature is increased. To understand the experimental results, we have developed a reaction sequence between the various CnHm species, from ethylene to C monomers and dimers, based on ab initio density functional calculations of all the energy barriers and the Arrhenius prefactors for the most important processes. The resulting temperature evolution of all species obtained from the simulated kinetics of ethylene decomposition agrees with photoemission measurements. The molecular dissociation mechanism begins with the dehydrogenation of ethylene to vinylidene (CH2C), which is then converted to acetylene (CHCH) by the removal and addition of an H atom. The C-C bond is then broken to form methylidyne (CH), and in the same temperature range a small amount of ethylidyne (CH3C) is produced. Finally methylidyne dehydrogenates to produce C monomers that are available for the early stage nucleation of the graphene islands.

Journal article

Morgan S, Vvedensky D, Shah R, Girardi T, Newschaffer C, Katzman P, Miller R, Moye J, Salafia Cet al., 2016, ARTERIAL CHORIONIC SURFACE VESSEL BRANCH POINT DENSITY AND AUTISM RISK, Meeting of the International-Federation-of-Placenta-Associations (IFPA) - Placenta-Back to the Basics, Publisher: W B SAUNDERS CO LTD, Pages: 74-74, ISSN: 0143-4004

Conference paper

Schubert D, Leonard A, Lee J, Morgan S, Vvedensky D, Newschaffer C, Shah R, Miller R, Katzman P, Moye J, Salafia Cet al., 2016, FAMILIAL HIGH ASD RISK DIFFERS FROM A LOW RISK COHORT BY LONGER SEGMENT LENGTHS AND POTENTIAL REDUCED BRANCHING IN EARLY BUT NOT LATER BRANCH GENERATIONS, Meeting of the International-Federation-of-Placenta-Associations (IFPA) - Placenta-Back to the Basics, Publisher: W B SAUNDERS CO LTD, Pages: 74-75, ISSN: 0143-4004

Conference paper

Westbroek MJE, King PR, Vvedensky DD, 2016, Path Integral Method for Flow through Random Porous Media

One of the key problems in modelling flow in oil reservoirs is our lack of precise knowledge of the variations in flow properties across the field. At best we can infer the statistics of these variations from field observations. The challenge is to determine the statistics of the flow itself (flow rates, pressures etc.) from the statistics of the permeability variations. Conventional simulations are computationally very expensive unless smart sampling techniques or surrogate models are used. In this paper we demonstrate the use of a path integral formulation for this problem. To demonstrate how this methods works, we start with the one dimensional Darcy flow problem: q(x)=-K(x)dp(x)/dx where p(x) is the pressure, q(x) is the flow rate and K(x) is the rock permeability. The randomness of the porous medium is modelled by regarding K as a stochastic quantity which is assumed to follow Gaussian statistics. Because of the randomly varying rock structure, there is a variety of conceivable pressure realisations p(x). The path integral Z is an integral over all realisations with an appropriate probability measure. Once Z is evaluated, either analytically, or by standard Monte Carlo methods, any observable of interest, including pressure correlations can be easily obtained.

Conference paper

Westbroek MJE, King PR, Vvedensky DD, 2016, Path Integral Method for Flow through Random Porous Media

One of the key problems in modelling flow in oil reservoirs is our lack of precise knowledge of the variations in flow properties across the field. At best we can infer the statistics of these variations from field observations. The challenge is to determine the statistics of the flow itself (flow rates, pressures etc.) from the statistics of the permeability variations. Conventional simulations are computationally very expensive unless smart sampling techniques or surrogate models are used. In this paper we demonstrate the use of a path integral formulation for this problem. To demonstrate how this methods works, we start with the one dimensional Darcy flow problem: q(x)=-K(x)dp(x)/dx where p(x) is the pressure, q(x) is the flow rate and K(x) is the rock permeability. The randomness of the porous medium is modelled by regarding K as a stochastic quantity which is assumed to follow Gaussian statistics. Because of the randomly varying rock structure, there is a variety of conceivable pressure realisations p(x). The path integral Z is an integral over all realisations with an appropriate probability measure. Once Z is evaluated, either analytically, or by standard Monte Carlo methods, any observable of interest, including pressure correlations can be easily obtained.

Conference paper

Moroni S, Dimastrodonato V, Chung T-H, Juska G, Gocalinska A, Vvedensky D, Pelucchi Eet al., 2016, Modeling InGaAs MOVPE in v-grooves and pyramidal recesses, 28th International Conference on Indium Phosphide & Related Materials (IPRM) / 43rd International Symposium on Compound Semiconductors (ISCS), Publisher: IEEE

Conference paper

Edmunds DM, Tangney P, Vvedensky DD, Foulkes WMCet al., 2015, Free-energy coarse-grained potential for C60, Journal of Chemical Physics, Vol: 143, Pages: 164509-1-164509-4, ISSN: 0021-9606

We propose a new deformable free energy method for generating a free-energy coarse-graining potential for C60. Potentials generated from this approach exhibit a strong temperature dependence and produce excellent agreement with benchmark fully atomistic molecular dynamics simulations. Parameter sets for analytical fits to this potential are provided at four different temperatures.

Journal article

Moroni ST, Dimastrodonato V, Chung T-H, Juska G, Gocalinska A, Vvedensky DD, Pelucchi Eet al., 2015, Indium segregation during III-V quantum wire and quantum dot formation on patterned substrates, JOURNAL OF APPLIED PHYSICS, Vol: 117, ISSN: 0021-8979

Journal article

Tetlow H, de Boer JP, Ford IJ, Vvedensky DD, Coraux J, Kantorovich Let al., 2014, Growth of epitaxial graphene: Theory and experiment, PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS, Vol: 542, Pages: 195-295, ISSN: 0370-1573

Journal article

de Boer JP, Ford IJ, Kantorovich L, Vvedensky DDet al., 2014, Optimization algorithm for rate equations with an application to epitaxial graphene, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 26, ISSN: 0953-8984

Journal article

Gocalinska A, Manganaro M, Juska G, Dimastrodonato V, Thomas K, Joyce BA, Zhang J, Vvedensky DD, Pelucchi Eet al., 2014, Unusual nanostructures of "lattice matched" InP on AlInAs, Applied Physics Letters, Vol: 104, ISSN: 0003-6951

ABSTRACTWe show that the morphology of the initial monolayers of InP on Al0.48In0.52As grown by metalorganic vapor-phase epitaxy does not follow the expected layer-by-layer growth mode of lattice-matched systems, but instead develops a number of low-dimensional structures, e.g., quantum dots and wires. We discuss how the macroscopically strain-free heteroepitaxy might be strongly affected by local phase separation/alloying-induced strain and that the preferred aggregation of adatom species on the substrate surface and reduced wettability of InP on AlInAs surfaces might be the cause of the unusual (step) organization and morphology.The formation of interfaces with structural, compositional, and morphological integrity is crucial for the performance of many devices. Imperfect interfaces produce broadening in photoluminescence line widths and degrade electronic transport by enhanced scattering. Structure and morphology can be optimized through controlled sample preparation and a judicious choice of growth conditions. However, while semiconductor alloys enable band gaps to be engineered, the attainment of compositional uniformity presents altogether different challenges. Indeed, in III–V systems, phase separation is common when alloys are deposited onto a lattice-matched substrate, for example, by molecular-beam epitaxy (MBE).1 Our focus here is Al1−xInxAs, a large band-gap (lattice-matched) material used in heterostructures with InP. When produced by MBE (in specific, but a relatively large range of growth conditions), this alloy is known to exhibit clustering when deposited onto InP.2,3 Interestingly, theoretical studies4,5 have shown that this type of incipient spinodal decomposition is forbidden if the surface of the alloy film is perfectly flat because of the regions of additional strain created with respect to the random alloy, which has zero mean strain everywhere. But on a surface with roughness, phase separation can become more active at roughness-i

Journal article

Gill JS, Woods MP, Salafia CM, Vvedensky DDet al., 2014, Probability distributions for measures of placental shape and morphology, PHYSIOLOGICAL MEASUREMENT, Vol: 35, Pages: 483-500, ISSN: 0967-3334

Journal article

Gocalinska A, Manganaro M, Juska G, Dimastrodonato V, Thomas K, Joyce BA, Zhang J, Vvedensky DD, Pelucchi Eet al., 2014, InP-AlInAs "strain free" early stages heteroepitaxy leading to nanostructure formation by MOVPE, 26th International Conference on Indium Phosphide and Related Materials (IPRM), Publisher: IEEE, ISSN: 1092-8669

Conference paper

Dimastrodonato V, Pelucchi E, Zestanakis PA, Vvedensky DDet al., 2013, Morphological, compositional, and geometrical transients of V-groove quantum wires formed during metalorganic vapor-phase epitaxy, APPLIED PHYSICS LETTERS, Vol: 103, ISSN: 0003-6951

Journal article

Dimastrodonato V, Pelucchi E, Zestanakis PA, Vvedensky DDet al., 2013, Transient and self-limited nanostructures on patterned surfaces, PHYSICAL REVIEW B, Vol: 87, ISSN: 2469-9950

Journal article

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