arXiv subjects

Predrag S. Krstic

Publications and source records attributed to Predrag S. Krstic.

5 recordsLinked to original sources

arXiv2025

Suitability of ReaxFF potential for MD modelling of lithium across low and high temperatures

Modeling lithium's atomic-scale behavior is critical for its roles in plasma-facing fusion components and lithium-ion batteries, yet it remains challenging across phase regimes. This study benchmarks ReaxFF, 2NN-MEAM, and SNAP potentials from 100 to 1000 K using molecular dynamics, with ensemble and cooling protocols carefully controlled. Compared to reliable experimental data, ReaxFF diverges above 800 K, underestimating density by ~10% at 1000 K and overestimating diffusivity, yielding anomalously low-density liquid behavior. Radial distribution functions and coordination profiles further reveal possible excessive disorder above 800 K. While ReaxFF offers qualitative insight into disordered lithium, its quantitative reliability diminishes at high temperatures, requiring validation against ab initio or experimental benchmarks. These findings inform potential selections for fusion- and battery-relevant simulations, underscoring the sensitivity of glassy phase modeling to potential choices and thermal histories.

physics.chem-ph↗

arXiv2023

Collisional S-Matrix for the Vibrational Dynamics of H+H2 by Quantum Computing

An algorithm and a system of quantum circuits is developed and applied to compute accurately the S matrix for the transitions between vibrational states of H2 for collisions with H. The algorithm was applied to 100 eV laboratory collision energy at a quantum circuit simulator. The effects of the discretized dissociative continuum to the transition cross sections are carefully studied and accuracy and convergence of the results with the chosen parameters of the algorithm and the collision system are verified by comparison with a solution of the time-dependent Schrodinger equation using the classical algorithm as well as comparison with a few results from the literature.

quant-ph↗

arXiv2022

Multistate Transition Dynamics by Strong Time-Dependent Perturbation in NISQ era

We develop a quantum computing scheme utilizing McLachlan variational principle in a hybrid quantum-classical algorithm to accurately calculate the transition dynamics of a closed quantum system with many excited states subject to a strong time-dependent perturbation. A systematic approach for optimal construction of a general N-state ansatz with unary N-qubit encoding is refined. We also utilize qubit efficient encoding in McLachlan variational quantum algorithm to reduce the number of qubits to log2 N, simultaneously diminishing depths of the quantum circuits. The significant reduction of the number of time steps is achieved by use of the second order marching method. Instrumental in obtaining high accuracy are adaptations of the circuits to include time-dependent global phase correction. We illustrated, tested and optimized our quantum computing algorithm on a set of 16 bound hydrogenic eigenstates exposed to a strong laser attosecond pulse. Results for transition probabilities are obtained with accuracy better than 1%, as established by comparison to the benchmark data. Use of interaction representation of the Hamiltonian reduces the effect of both NISQ noise and sampling errors accumulation while the quantum system evolves in time.

quant-ph↗

arXiv2020

Prospect of using Grover's search in the noisy-intermediate-scale quantum-computer era

In order to understand the bounds of utilization of the Grover's search algorithm for the large unstructured data in presence of the quantum computer noise, we undertake a series of simulations by inflicting various types of noise, modelled by the IBM QISKit. We apply three forms of Grover's algorithms: (1) the standard one, with 4-10 qubits, (2) recently published modified Grover's algorithm, set to reduce the circuit depth, and (3) the algorithms in (1) and (2) with multi-control Toffoli's modified by addition of an ancilla qubit. Based on these simulations, we find the upper bound of noise for these cases, establish its dependence on the quantum depth of the circuit and provide comparison among them. By extrapolation of the fitted thresholds, we predict what would be the typical gate error bounds when apply the Grover's algorithms for the search of a data in a data set as large as thirty two thousands.

quant-ph↗

arXiv2004

Rate Coefficient for H^+ + H_2(X ^1Sigma_g^+, nu=0, J=0) --> H(1s) + H_2^+ Charge Transfer and Some Cosmological Implications

Krstic has carried out the first quantum mechanical calculations near threshold for the charge transfer (CT) process H^+ + H_2(X ^1Sigma_g^+, nu=0, J=0) --> H(1s) + H_2^+. These results are relevant for models of primordial galaxy and first star formation that require reliable atomic and molecular data for obtaining the early universe hydrogen chemistry. Using the results of Krstic, we calculate the relevant CT rate coefficient for temperatures between 100 and 30,000 K. We also present a simple fit which can be readily implemented into early universe chemical models. Additionally, we explore how the range of previously published data for this reaction translates into uncertainties in the predicted gas temperature and H_2 relative abundance in a collapsing primordial gas cloud. Our new data significantly reduce these cosmological uncertainties that are due to the uncertainties in the previously published CT rate coefficients.

astro-ph↗