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Payam Kaghazchi

Publications and source records attributed to Payam Kaghazchi.

5 recordsLinked to original sources

Accelerated Prediction of Surface Stability and Particle Morphology in Ionic Crystals via Electrostatic Screening

This work presents a fast and scalable approach for predicting surface stability and equilibrium crystal morphology in ionic materials using electrostatic analysis. The method constructs stoichiometric slab terminations and evaluates their electrostatic energies, enabling high-throughput screening of surface configurations at a fraction of the cost of conventional approaches. Polar surfaces are identified through surface dipole moment calculations and stabilized via electrostatics-based reconstruction using replica-exchange Monte Carlo simulations. The surface dipole moment further emerges as an effective descriptor to distinguish the behavior of different classes of materials. By bypassing expensive Density Functional Theory (DFT) calculations, the approach extends naturally to large systems and high-index surfaces that are typically inaccessible to DFT. Electrostatic interactions are shown to capture the dominant trends in relative surface stability across diverse material systems. The method is validated on simple and complex 3D materials as well as 2D layered oxides, where the predicted dominant facets are consistent with reported density functional theory and experimental observations. Importantly, the framework also reveals cases where high-index surfaces play a non-negligible role in the equilibrium morphology. These results establish electrostatics as a fast and reliable route for high-throughput prediction of surface stability and particle morphology, opening a pathway for accelerated materials discovery and providing a robust starting point for more detailed calculations in complex energy materials.

cond-mat.mtrl-sci

Computational Studies on O2-P2 Phase-Transition Dynamics in Layered-Oxide Sodium-Ion Cathode Materials

Sodium-ion batteries have gained much interest over the past years and especially layered oxides are highly considered as cathodes for the next generation of batteries. However, there are still significant challenges to overcome in these materials for practical applications mainly related to capacity degradation and voltage fading. A key influence factor for these challenges are phase transitions that occur by gliding of layers during operation of these materials. Until now there is limited atomistic-level understanding on such transitions as simulations of these processes are computationally demanding. In this work, we trained a classical pairwise Coulomb-Buckingham potential versus extensive \textit{ab initio} data using a genetic algorithm to study O2-P2 phase transitions in Na\textsubscript{\textit{x}}CoO\textsubscript{2}. Our density functional theory~(DFT) and classical potential calculations show that phase transition barriers decrease upon desodiation and are further lowered if dynamic conditions are considered through molecular dynamics simulations. Our developed classical potential is able to capture phase transitions and its related increase in the Na-ion diffusivity under standard lab conditions at the $\upmu$s timescale of molecular dynamics simulation. Furthermore, it is found that the phase transition occurs gradually \textit{via} various OP\textit{n} phases.

cond-mat.mtrl-sci

Simulating charging characteristics of lithium iron phosphate by electro-ionic optimization on a quantum annealer

The rapid evolution of quantum computing hardware opens up new avenues in the simulation of energy materials. Today's quantum annealers are able to tackle complex combinatorial optimization problems. A formidable challenge of this type is posed by materials with site-occupational disorder for which atomic arrangements with a low, or lowest, energy must be found. In this article, a method is presented for the identification of the correlated ground-state distribution of both lithium ions and redox electrons in lithium iron phosphate (LFP), a widely employed cathode material in lithium-ion batteries. The point-charge Coulomb energy model employed correctly reproduces the LFP charging characteristics. As is shown, grand-canonical transformation of the energy cost function makes the combinatorial distribution problem solvable on quantum annealing (QA) hardware. The QA output statistics follow a pseudo-thermal behavior characterized by a problem-dependent effective sampling temperature, which has bearings on the estimated scaling of the QA performance with system size. This work demonstrates the potential of quantum computation for the joint optimization of electronic and ionic degrees of freedom in energy materials.

cond-mat.mtrl-sci

Optimization of Coulomb Energies in Gigantic Configurational Spaces of Multi-Element Ionic Crystals

Most of the novel energy materials contain multiple elements occupying a single site in their lattice. The exceedingly large configurational space of these materials imposes challenges in determining their ground-state structures. Coulomb energies of possible configurations generally show a satisfactory correlation to computed energies at higher levels of theory and thus allow to screen for minimum-energy structures. Employing a second-order cluster expansion, we obtain an efficient Coulomb energy optimizer using Monte Carlo and Genetic Algorithms. The presented optimization package, GOAC (Global Optimization of Atomistic Configurations by Coulomb), can achieve a speed up of several orders of magnitude compared to existing software. Our code is able to find low-energy configurations of complex systems involving up to $10^{920}$ structural configurations. The GOAC package thus provides an efficient method for constructing ground-state atomistic models for multi-element materials with gigantic configurational spaces.

cond-mat.mtrl-sci

Influence of elastic strain on the thermodynamics and kinetics of lithium vacancy in bulk LiCoO2

The influence of elastic strain on the lithium vacancy formation and migration in bulk LiCoO2 is evaluated by means of first-principles calculations within density functional theory (DFT). Strain dependent energies are determined directly from defective cells and also within linear elasticity theory from the elastic dipole tensor (Gij) for ground state and saddle point configurations. We analyze finite size-effects in the calculation of Gij, compare the predictions of the linear elastic model with those obtained from direct calculations of defective cells under strain and discuss the differences. Based on our data, we calculate the variations in vacancy concentration and mobility due to the presence of external strain in bulk LiCoO2 cathodes. Our results reveal that elastic in-plane and out-of-plane strains can significantly change the ionic conductivity of bulk LiCoO2 by an order of magnitude and thus strongly affect the performance of Li-secondary batteries.

cond-mat.mtrl-sci