arXiv subjects

Wan-Lu Li

Publications and source records attributed to Wan-Lu Li.

10 recordsLinked to original sources

arXiv2025

KVFlow: Efficient Prefix Caching for Accelerating LLM-Based Multi-Agent Workflows

Large language model (LLM) based agentic workflows have become a popular paradigm for coordinating multiple specialized agents to solve complex tasks. To improve serving efficiency, existing LLM systems employ prefix caching to reuse key-value (KV) tensors corresponding to agents' fixed prompts, thereby avoiding redundant computation across repeated invocations. However, current systems typically evict KV caches using a Least Recently Used (LRU) policy, which fails to anticipate future agent usage and often discards KV caches shortly before their reuse. This leads to frequent cache misses and substantial recomputation or swapping overhead. We present KVFlow, a workflow-aware KV cache management framework tailored for agentic workloads. KVFlow abstracts the agent execution schedule as an Agent Step Graph and assigns each agent a steps-to-execution value that estimates its temporal proximity to future activation. These values guide a fine-grained eviction policy at the KV node level, allowing KVFlow to preserve entries likely to be reused and efficiently manage shared prefixes in tree-structured caches. Moreover, KVFlow introduces a fully overlapped KV prefetching mechanism, which proactively loads required tensors from CPU to GPU in background threads for agents scheduled in the next step, thereby avoiding cache miss stalls during generation. Compared to SGLang with hierarchical radix cache, KVFlow achieves up to 1.83$\times$ speedup for single workflows with large prompts, and up to 2.19$\times$ speedup for scenarios with many concurrent workflows.

cs.DC↗

arXiv2025

Computational Analysis of Interface-Driven Spin-Orbit Coupling in Molecular Adsorbates on Transition Metal Dichalcogenides

Spin-orbit coupling (SOC) lifts molecular orbital degeneracy, enabling bi-level electronic platforms suitable for next-generation digital devices. However, common light-atom molecular feedstocks exhibit weak SOC due to the absence of heavy elements. To enhance SOC without synthesizing new materials, we leverage interfacial interactions between molecules and transition-element-based solid-state materials. This computational study investigates SOC splitting in metal-phthalocyanine adsorbed on transition metal dichalcogenides (TMDs) using density functional theory (DFT). The enhanced SOC splitting is attributed to strong orbital hybridization at the molecule-substrate interface. Specifically, Zn-phthalocyanine (ZnPC) on monolayer MoS2 achieves a notable SOC splitting of ~8 meV. Furthermore, when ZnPC forms self-assembled chains on MoS2, the splitting increases to ~20 meV, driven by the formation of hybrid bands modulated by molecular periodicity. These findings highlight the role of interfacial and intermolecular interactions in inducing and enhancing SOC in surface-adsorbed molecules, providing a new strategy for molecular spintronic materials without complex synthetic efforts.

cond-mat.mtrl-sci↗

arXiv2025

Ammonia Synthesis under Ambient Conditions: Insights into Water-Nitrogen-Magnetite Interfaces

New routes for transforming nitrogen into ammonia at ambient conditions would be a milestone toward an energy efficient and economically attractive production route in comparison to the traditional Haber-Bosch process. Recently, the synthesis of ammonia from water and nitrogen at room temperature and atmospheric pressure has been reported to be catalyzed by Fe3O4 at the air-water interface. By integrating ambient pressure X-ray photoelectron spectroscopy and ab initio molecular dynamics and free energy calculations, we investigate the underlying thermodynamic mechanisms governing ammonia and hydrazine formation at the water-Fe3O4-nanoparticle interface. We find that, unlike pure Fe3O4 where N2 can only interact with a limited number of Fe sites, hydroxylated species introduce large and diverse adsorption geometries where N2 can bind through either Fe sites or Fe-OH groups, each of which are capable of independently facilitating proton-coupled electron transfer.

physics.chem-ph↗

arXiv2025

Boron-assisted synthesis of compositionally complex amorphous oxides via short-range-order-constrained generative design

Engineering short-range atomic order in amorphous materials offers a promising yet still underexplored route to high-performance solids. Here, we establish a boron-assisted amorphization strategy through ApolloX, a theory-guided, short-range-order-constrained generative framework for identifying low-energy amorphous configurations in compositionally complex multimetal BOx systems. Using FeCoNiMoBOx as a representative model platform, ApolloX predicts an ensemble of candidate amorphous configurations across systematically varied boron contents. Ab initio molecular dynamics simulations based on these configurations show that increasing boron content suppresses atomic diffusion and disfavors crystallization, with the stabilization of BO3-centered local motifs emerging as a key structural feature associated with enhanced amorphization propensity. Guided by these predictions, we synthesize three representative FeCoNiMoBOx compositions with distinct boron contents and use synchrotron-based scattering and electron microscopy to verify compositional fidelity, structural homogeneity, and the targeted amorphous features, thereby experimentally validating the boron-regulated structural evolution predicted by theory. Beyond this representative system, the same strategy is extended to a broader library of multimetal BOx amorphous compositions spanning diverse metal combinations and boron loadings, demonstrating that the boron-assisted route is not limited to a single FeCoNiMoBOx family but is broadly transferable across compositionally complex amorphous oxides. Overall, our results establish boron incorporation as a practical design variable for tuning short-range order and amorphization in multicomponent oxides, and provide a general framework for the theory-guided discovery of compositionally complex amorphous materials with tunable properties.

cond-mat.mtrl-sci↗

arXiv2024

Characterization of Coulomb Interactions in Electron Transport through a Single Hetero-Helicene Molecular Junction Using Scanning Tunneling Microscopy

Characterization of the structural and electron transport properties of single chiral molecules provides critical insights into the interplay between their electronic structure and electrochemical environments, providing broader implications given the significance of molecular chirality in chiroptical applications and pharmaceutical sciences. Here, we examined the topographic and electronic features of a recently developed chiral molecule, B,N-embedded double hetero[7]helicene, at the edge of Cu(100) supported NaCl thin film with scanning tunneling microscopy and spectroscopy. An electron transport energy gap of 3.2 eV is measured, which is significantly larger than the energy difference between the highest occupied and the lowest unoccupied molecular orbitals given by theoretical calculations or optical measurements. Through first principles calculations, we demonstrated that this energy discrepancy results from the Coulomb interaction between the tunneling electron and the molecule's electrons. This occurs in electron transport processes when the molecule is well decoupled from the electrodes by the insulating decoupling layers, leading to a temporary ionization of the molecule during electron tunneling. Beyond revealing properties concerning a specific molecule, our findings underscore the key role of Coulomb interactions in modulating electron transport in molecular junctions, providing insights into the interpretation of scanning tunneling spectroscopy features of molecules decoupled by insulating layers.

physics.chem-ph↗

arXiv2024

Operating a Multi-Level Molecular Dimer Switch through Precise Tip-Molecule Control

Controlling structural transitions between molecular configurations is crucial for advancing functional molecular electronics. While reversible switching of bistable two-state molecules has been achieved, creating molecular systems that can be controllably switched between multiple configurations often requires complex synthetic methods, presenting a much greater challenge. In this study, we showcase a straightforward yet effective strategy to create and control transitions between multiple molecular structural states by forming a surface-bound molecular dimer. Using low-temperature scanning tunneling microscopy, we induce and characterize the structural transitions of a pyrrolidine dimer on a Cu(100) surface. The intermolecular interactions open new energy transfer channels, enabling the excitation through pathways that were inaccessible in monomers. The occupation of different molecular states is highly sensitive to both the energy of the tunneling electrons and the interaction with the STM tip. By precisely adjusting the tip-molecule distance, we can select the most probable structural configuration based on sample bias, thereby achieving on-demand control of this molecular dimer switch. This work highlights an approach that leverages both intermolecular and molecule-environment interactions to create and control an artificially fabricated molecular device.

physics.chem-ph↗

arXiv2023

Greater Transferability and Accuracy of Norm-conserving Pseudopotentials using Nonlinear Core Corrections

We present an investigation into the transferability of pseudopotentials (PPs) with a nonlinear core correction (NLCC) using the Goedecker, Teter, and Hutter (GTH) protocol across a range of pure GGA, meta-GGA and hybrid functionals, and their impact on thermochemical and non-thermochemical properties. The GTH-NLCC PP for the PBE density functional demonstrates remarkable transferability to the PBE0 and $ω$B97X-V exchange-correlation functionals, and relative to no NLCC, improves agreement significantly for thermochemical benchmarks compared to all-electron calculations. On the other hand, the B97M-rV meta-GGA functional performs poorly with the PBE-derived GTH-NLCC PP, which is mitigated by reoptimizing the NLCC parameters for this specific functional. The findings reveal that atomization energies exhibit the greatest improvements from use of the NLCC, which thus provides an important correction needed for covalent interactions relevant to applications involving chemical reactivity. Finally we test the NLCC-GTH PPs when combined with medium-size TZV2P molecularly optimized (MOLOPT) basis sets which are typically utilized in condensed phase simulations, and show that they lead to consistently good results when compared to all-electron calculations for atomization energies, ionization potentials, barrier heights, and non-covalent interactions, but lead to somewhat larger errors for electron affinities.

physics.chem-ph↗

arXiv2020

The Critical Role of Thermal Fluctuations for Electrocatalytic Metal Surface Properties and CO Binding Trends

This work addresses a longstanding theoretical discrepancy using Density Functional Theory (DFT) with experimental observations of CO binding trends on electrocatalytically relevant metals for the CO2 reduction reaction (CO2RR). By introducing thermal fluctuations using appropriate statistical mechanical NVT and NPT ensembles, we show that DFT with universal dispersion interactions yields qualitatively better metal surface strain trends and CO binding energetics, consistently predicts the correct site preference for all metals due to thermally induced surface distortions that preferentially exposes the undercoordinated atop site for Cu(111) and Pt(111), and for the weak binding Ag(111) and Au(111) surfaces at finite temperatures shows CO-metal interactions that are a mixture of chemisorbed and physisorbed species. This study better places theory as an equal partner to experimental heterogeneous catalysis by demonstrating the need to fully account for finite temperature fluctuations to make contact with surface science experiments.

physics.chem-ph↗

arXiv2020

An Isolated Water Droplet in the Aqueous Solution of a Supramolecular Tetrahedral Cage

Water under nanoconfinement at ambient conditions has exhibited low-dimensional ice formation and liquid-solid phase transitions, but with structural and dynamical signatures which map onto known regions of waters phase diagram. Using THz absorption spectroscopy and ab initio molecular dynamics, we have investigated the ambient water confined in a supramolecular tetrahedral assembly, and determined that a distinct network of 9-10 water molecules is present within the nanocavity of the host. The low-frequency absorption spectrum and theoretical analysis of the water in the $Ga_4$$L_6$$^{-12}$ host demonstrate that the structure and dynamics of the encapsulated droplet is distinct from any known phase of water. A further inference is that the release of the highly unusual encapsulated water droplet creates a strong thermodynamic driver for the high affinity binding of guests in aqueous solution for the $Ga_4$$L_6$$^{-12}$ supramolecular construct.

physics.chem-ph↗

arXiv2019

Interplay of Water and a Supramolecular Capsule for Catalysis of Reductive Elimination Reaction from Gold

Supramolecular assemblies have gained tremendous attention due to their apparent ability to catalyze reactions with the efficiencies of natural enzymes. Using Born-Oppenheimer molecular dynamics and density functional theory, we identify the origin of the catalytic power of the supramolecular assembly Ga$_4$L$_{612-}$ on the reductive elimination reaction from gold complexes and their similarity to enzymes. By comparing the catalyzed and uncatalyzed reaction in explicit solvent to identify the reaction free energies of the reactants, transition states, and products, we determine that a catalytic moiety -- an encapsulated water molecule -- generates electric fields that contribute significant reduction in the activation free energy. Although this is unlike the biomimetic scenario of catalysis through direct host-guest interactions, the nanocage host preconditions the transition state for greater sensitivity to electric field projections onto the breaking carbon bonds to complete the reductive elimination reaction with greater catalytic efficiency. However it is also shown that the nanocage poorly organizes the interfacial water, which in turn creates electric fields that misalign with the breaking bonds of the substrate, thus identifying new opportunities for catalytic design improvements in nanocage assemblies.

physics.chem-ph↗