About

Professor Rajiv Kalia is a faculty member at the University of Southern California, serving as a Professor of Physics and Astronomy, Computer Science, Chemical Engineering and Materials Science, and Biomedical Engineering. His role involves interdisciplinary research and teaching across these fields, contributing to the university's efforts in advanced computing and simulations. The page indicates his association with the Collaboratory for Advanced Computing and Simulations, emphasizing his involvement in computational research and innovation.

Research topics

• Materials science
• Chemistry
• Organic chemistry
• Chemical engineering
• Nanotechnology
• Optoelectronics
• Physics
• Metallurgy
• Atomic physics
• Optics
• Molecular physics
• Composite material
• Quantum mechanics

Selected publications

• Emerging Ferroelectric Domains: Stacking and Rotational Landscape of MoS ₂ Moiré Bilayers

  ACS Nano · 2026-02-06

  article

  The structures and properties of moiré patterns in the twisted bilayers of two-dimensional (2D) materials are known to depend sensitively on the twist angle, yet their dependence on the stacking order remains comparatively underexplored. In this study, we use molecular dynamics simulations to systematically investigate the combined effects of the stacking order and rotation in MoS2 bilayers. Beginning from five well-established high-symmetry bilayer stackings, we apply twist angles between 1° and 120° to the top layer, revealing a variety of relaxed moiré structures. Our results show that the initial stacking significantly influences the moiré domain configurations that emerge at a given twist angle. While all five stacking orders are metastable without twist, they form two moiré-equivalent classes, AA/AB and AA′/A′B/AB′, i.e., for a given twist angle, structures within each class relax to the same moiré configuration. Specifically, initial AA and AB stackings give rise to triangular ferroelectric domains near 0 ± 3°, while AA′, A′B, and AB′ stackings produce triangular ferroelectric domains near 60 ± 3°. At precisely 60° and 120° twists, the bilayers relax into pure high-symmetry stackings, highlighting the rotational relationships between these configurations and explaining the shift of 60° in the ferroelectric rotational range. These findings demonstrate the critical role of the stacking order in governing the rich moiré landscapes accessible in twistronic systems.

  PublisherDOI

• High-temperature memristors enabled by interfacial engineering

  Science · 2026-03-26

  article

  Nonvolatile memories (NVMs) that operate reliably at high temperatures are essential for electronics in extreme environments. Here, we report graphene (Gra)/HfO x /tungsten (W) memristors that operated reliably up to 700°C, with an ON/OFF current ratio of >10 3 , data retention >50 hours, and endurance >10 9 switching cycles. Transmission electron microscopy revealed substantial W diffusion into the inert platinum (Pt) electrode in conventional Pt/HfO x /W memristors after high-temperature annealing, which was responsible for the thermal failure in conventional devices but not observed in Gra/HfO x /W devices. First-principles calculations attributed the enhanced thermal stability to weaker W adsorption and higher surface diffusion barriers on Gra compared with metals such as Pt. These results underscore the critical role of interfacial engineering and the potential of two-dimensional materials for enabling reliable high-temperature NVM technologies.

  PublisherDOI

• Supercritical water at ten densities from 0.1 to 1.0 gr/cc at 1000 K using <i>ab initio</i> molecular dynamics simulations

  The Journal of Chemical Physics · 2026-01-08

  articleOpen access

  Supercritical water is found inside Earth's mantle, where water is subjected to very high temperatures and pressures. It exhibits extraordinary properties, such as having a low dielectric constant and high reactivity, which stems from the breakdown of the hydrogen bond network in a supercritical state. This makes supercritical water a non-polar solvent and the basis for many innovative technologies. We investigate supercritical water at ten densities (0.1-1.0 gr/cc) at 1000 K to study the structural correlations, such as atom-resolved partial pair distributions, co-ordination numbers, bond-angle distributions and neutron scattering, and x-ray structure factors. Among the dynamical correlations, we investigate the velocity autocorrelation function, current-current correlation function, and their Fourier transforms-vibrational density-of-states and frequency dependent dielectric constant. Structural and dynamical correlations are computed from time-trajectories of the positions and velocities calculated ab initio molecular dynamics within the density functional theory framework using the SCAN exchange-correlation functional. Our results for structural correlations are compared with the neutron scattering experiments on supercritical water by Soper and collaborators [J. Chem. Phys. 106, 247-254 (1997)] and dynamical correlations in the supercritical state are compared with the inelastic neutron scattering results by Car and collaborators [J. Phys. Chem. Lett. 11, 9461-9467 (2020)].

  PublisherDOI

• Multiscale light-matter dynamics in quantum materials: from electrons to topological superlattices

  ArXiv.org · 2025-08-31

  preprintOpen access

  Light-matter dynamics in topological quantum materials enables ultralow-power, ultrafast devices. A challenge is simulating multiple field and particle equations for light, electrons, and atoms over vast spatiotemporal scales on Exaflop/s computers with increased heterogeneity and low-precision focus. We present a paradigm shift that solves the multiscale/multiphysics/heterogeneity challenge harnessing hardware heterogeneity and low-precision arithmetic. Divide-conquer-recombine algorithms divide the problem into not only spatial but also physical subproblems of small dynamic ranges and minimal mutual information, which are mapped onto best-characteristics-matching hardware units, while metamodel-space algebra minimizes communication and precision requirements. Using 60,000 GPUs of Aurora, DC-MESH (divide-and-conquer Maxwell-Ehrenfest-surface hopping) and XS-NNQMD (excited-state neural-network quantum molecular dynamics) modules of MLMD (multiscale light-matter dynamics) software were 152- and 3,780-times faster than the state-of-the-art for 15.4 million-electron and 1.23 trillion-atom PbTiO3 material, achieving 1.87 EFLOP/s for the former. This enabled the first study of light-induced switching of topological superlattices for future ferroelectric 'topotronics'.

  PublisherOA PDFDOI

• A Route to Design Novel Functional Peptides by Applying a Denoising Diffusional Model to mRNA Display Libraries

  ChemBioChem · 2025-10-28 · 1 citations

  articleOpen accessCorresponding

  In vitro directed evolution techniques, such as mRNA display, enable peptide ligand discovery and optimization. However, physical libraries that rely on a genetic code can only search a small fraction of sequence space due to inherent biases in the genetic code and experimental limitations. To address this challenge, denoising diffusion implicit models (DDIMs) are applied to generate novel peptide ligands against B‐cell lymphoma extra‐large (Bcl‐x L ), a key cancer target. Starting with high‐throughput sequencing data from previous selections, a DDIM is trained to produce novel sequences with high affinity binding. Experimental validation confirms that most generated sequences are functionally equivalent to the original library members for Bcl‐x L binding and demonstrated comparable binding kinetics and affinity relative to the wildtype and nearest original neighbors. Importantly, this approach generated rare sequences not easily accessible via mutation and directed evolution. These results indicate that DDIMs can complement and expand directed evolution data, efficiently exploring underrepresented regions of sequence space. This approach provides a broadly applicable framework for accelerating ligand discovery and optimizing molecular properties across diverse targets.

  PublisherOA PDFDOI

• Surface acoustic waves and lattice vibrations in two-dimensional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ti</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>T</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">O</mml:mi><mml:mo>,</mml:mo><mml:mo> </mml:mo><mml:mi mathvariant="normal">F</mml:mi><mml:mo>)</mml:mo></mml:math> MXene films

  Physical review. B./Physical review. B · 2025-06-02 · 1 citations

  articleOpen access

  We investigated surface acoustic wave (SAW) propagation and lattice vibrations in two-dimensional (2D) titanium carbide <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mo>(</a:mo><a:msub><a:mi>Ti</a:mi><a:mn>3</a:mn></a:msub><a:msub><a:mi mathvariant="normal">C</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>T</a:mi><a:mi mathvariant="normal">x</a:mi></a:msub><a:mo>)</a:mo></a:mrow></a:math> MXene films as a function of surface termination and layer stacking, using atomistic simulations. We found that SAW propagation velocity is highly sensitive to both single-layer properties and interlayer bonding. Surface terminations significantly modulate wave behavior, with oxygen and fluorine terminations producing distinct effects on wave propagation, with oxygen-terminated monolayers exhibiting 20% higher wave speeds than fluorine counterparts due to strengthened intralayer bonds. Key observations include the transition from one to two layers causing wave speed variations, and the development of interlayer modes that generate more dispersed lattice vibrations. As the film layer thickness increases, SAW propagation becomes predominantly confined to the upper surface, with coherence of vibrational modes diminishing in multilayer structures. These findings suggest MXene terminations and layer stacking are crucial parameters for controlling SAW behavior, offering promising avenues for novel acoustic wave device applications.

  PublisherOA PDFDOI

• Photochemistry and Thermal Chemistry in Polymeric Ceramic Precursors

  The Journal of Physical Chemistry Letters · 2025-09-11 · 1 citations

  article

  While pyrolysis of polymeric precursors has gained attention for the additive manufacturing of ceramics, the high-temperature process is energy-inefficient and time-consuming. Recently, photochemistry has been suggested to reduce energy consumption and reaction time, but the microscopic mechanisms of such accelerated reactions remain elusive. Here, we reveal distinct photochemical and thermal reaction pathways at the initial stage of silicon-carbide ceramic formation from an acylsilane precursor, using a multiscale simulation approach that combines first-principles nonadiabatic and adiabatic quantum molecular dynamics simulations with semiempirical reactive molecular dynamics simulations. While photoexcitation causes scission of Si-C bonds within 100 fs driven by the localization of a photoexcited hole, the precursor remains stable at high temperatures up to 1800 K without photoexcitation. On longer time scales, we find thermal reaction pathways involving concerted motions of many atoms, including the formation of SiCO clusters, mainly resulting from oxygen of carbonyl carbon shifting and bonding with silicon. This microscopic understanding suggests synergistic use of photochemical and thermal pathways to design ultralow-energy and facile additive manufacturing of ceramics toward achieving a sustainable society.

  PublisherDOI

• Emerging Ferroelectric Domains: Stacking and Rotational Landscape of MoS2 Moire Bilayers

  ArXiv.org · 2025-10-12

  preprintOpen access

  The structures and properties of moire patterns in twisted bilayers of two-dimensional (2D) materials are known to depend sensitively on twist angle, yet their dependence on stacking order remains comparatively underexplored. In this study, we use molecular dynamics simulations to systematically investigate the combined effects of stacking order and rotation in MoS2 bilayers. Beginning from five well-established high-symmetry bilayer stackings, we apply twist angles between 1 and 120 to the top layer, revealing a variety of relaxed moire structures. Our results show that the initial stacking significantly influences the moire domain configurations that emerge at a given twist angle. While all five stacking orders are metastable without twist, they form two moire-equivalent classes- AA/AB and AA',A'B,AB', i.e., for a given twist angle, structures within each class relax to the same moire configuration. Specifically, initial AA and AB stackings give rise to triangular ferroelectric domains near 0+/-3, while AA', A'B, and AB' stackings produce triangular ferroelectric domains near 60+/-3. At precisely 60 and 120 twists, the bilayers relax to into pure high-symmetry stackings, highlighting the rotational relationships between these configurations and explaining the shift of 60 in the ferroelectric rotational range. These findings demonstrate the critical role of stacking order in governing the rich moire landscapes accessible in twistronic systems.

  PublisherOA PDFDOI

• Allegro-FM: Toward an Equivariant Foundation Model for Exascale Molecular Dynamics Simulations

  The Journal of Physical Chemistry Letters · 2025-06-20 · 6 citations

  article

  We present a foundation model for exascale molecular dynamics simulations by leveraging an E(3) equivariant network architecture (Allegro) and a set of large-scale organic and inorganic materials data sets merged by the Total Energy Alignment framework. The obtained model (Allegro-FM) is versatile for various material simulations for diverse downstream tasks covering 89 elements in the training sets. Allegro-FM exhibits excellent agreement with high-level quantum chemistry theories in describing structural, mechanical, and thermodynamic properties, while exhibiting emergent capabilities for structural correlations, reaction kinetics, mechanical strengths, fracture, and solid/liquid dissolution, for which the model has not been trained. Furthermore, we demonstrate the robust predictability and generalizability of Allegro-FM for chemical reactions using Transition1x, which consists of tens of thousands of organic reactions and 9.6 million configurations including transition state data, in addition to reactive simulations using calcium silicate hydrates as a test bed. With its computationally efficient, strictly local network architecture, Allegro-FM scales up to multibillion-atom systems with a parallel efficiency of 0.975 on the exaflop/s Aurora supercomputer at Argonne Leadership Computing Facility. The approach presented in this work demonstrates the potential of the foundation model for novel materials design and discovery based on large-scale atomistic simulations.

  PublisherDOI

• Multiscale Light-Matter Dynamics in Quantum Materials: From Electrons to Topological Superlattices

  2025-11-12 · 1 citations

  articleOpen access

  Light-matter dynamics in topological quantum materials enables ultralow-power, ultrafast devices. A challenge is simulating multiple field and particle equations for light, electrons, and atoms over vast spatiotemporal scales on Exaflop/s computers with increased heterogeneity and low-precision focus. We present a paradigm shift that solves the multiscale/multiphysics/heterogeneity challenge harnessing hardware heterogeneity and low-precision arithmetic. Divide-conquer-recombine algorithms divide the problem into not only spatial but also physical subproblems of small dynamic ranges and minimal mutual information, which are mapped onto best-characteristics-matching hardware units, while metamodel-space algebra minimizes communication and precision requirements. Using 60,000 GPUs of Aurora, DC-MESH (divide-and-conquer Maxwell-Ehrenfest-surface hopping) and XS-NNQMD (excited-state neural-network quantum molecular dynamics) modules of MLMD (multiscale light-matter dynamics) software were 152- and 3,780-times faster than the state-of-the-art for 15.4 million-electron and 1.23 trillion-atom PbTiO3 material, achieving 1.87 EFLOP/s for the former. This enabled the first study of light-induced switching of topological superlattices for future ferroelectric ‘topotronics’.

  PublisherDOI

Frequent coauthors

• Priya Vashishta

  University of Southern California

  762 shared

• Aiichiro Nakano

  University of Southern California

  633 shared

• Fuyuki Shimojo

  205 shared

• Ken‐ichi Nomura

  University of Southern California

  106 shared

• Aravind Krishnamoorthy

  Texas A&M University

  95 shared

• Ankit Mishra

  University of Southern California

  69 shared

• Nitish Baradwaj

  University of Southern California

  64 shared

• Pankaj Rajak

  University of Southern California

  62 shared

Labs

• Collaboratory for Advanced Computing and SimulationsPI

Education

• Ph.D., Biomedical Engineering

  University of Southern California

  2000

• M.S., Biomedical Engineering

  University of Southern California

  1996

• B.S., Biomedical Engineering

  University of Southern California

  1994

Awards & honors

• Fellow of the American Physical Society
• Foundation for Fundamental Research on Matter (FOM) Fellowsh…
• Sustained Excellence Award in Ultra Dense, Ultra Fast Comput…
• USC Viterbi School of Engineering Senior Research Award
• 2000 FOM, The Netherlands Fellowship