Bath Configuration Research Articles

Advances in Parallel Heat Bath Configuration Interaction

Heat-bath configuration interaction (HCI) is a deterministic method that approaches the full CI limit at greatly reduced computational cost. In this work, computational improvements to the HCI algorithm are introduced targeting speed, parallel efficiency, and memory requirements. The new implementation introduces a hash function to distribute determinants and takes advantage of MPI and OpenMP for parallelism allowing for a (22e,168o) active space to be studied, which explicitly includes 2.39 × 107 variational determinants and 8.95 × 1010 perturbative determinants. Benchmarks show up to 86% parallel efficiency of the perturbative step on 32 nodes (4096 cores) and a total efficiency of 74%. The new HCI implementation is benchmarked for accuracy against prior results and applied to study the triplet-quintet gap in the challenging [FeO(NH3)5]2+ complex.

Near-exact nuclear gradients of complete active space self-consistent field wave functions.

In this paper, we study the nuclear gradients of heat bath configuration interaction self-consistent field (HCISCF) wave functions and use them to optimize molecular geometries for various molecules. We show that HCISCF nuclear gradients are fairly insensitive to the size of the "selected" variational space, which allows us to reduce the computational cost without introducing significant errors. The ability of the HCISCF to treat larger active spaces combined with the flexibility for users to control the computational cost makes the method very attractive for studying strongly correlated systems, which require a larger active space than possible with a complete active space self-consistent field. Finally, we study the realistic catalyst, Fe(PDI), and highlight some of the challenges this system poses for density functional theory (DFT). We demonstrate how HCISCF can clarify the energetic stability of geometries obtained from DFT when the results are strongly dependent on the functional. We also use the HCISCF gradients to optimize geometries for this species and study the adiabatic singlet-triplet gap. During geometry optimization, we find that multiple near-degenerate local minima exist on the triplet potential energy surface.

Trajectory Ensemble Methods Provide Single-Molecule Statistics for Quantum Dynamical Systems.

The emergence of experiments capable of probing quantum dynamics at the single-molecule level requires the development of new theoretical tools capable of simulating and analyzing these dynamics beyond an ensemble-averaged description. In this article, we present an efficient method for sampling and simulating the dynamics of the individual quantum systems that make up an ensemble and apply it to study the nonequilibrium dynamics of the ubiquitous spin-boson model. We generate an ensemble of single-system trajectories, and we analyze this trajectory ensemble using tools from classical statistical mechanics. Our results demonstrate that the dynamics of quantum coherence is highly heterogeneous at the single-system level due to variations in the initial bath configuration, which significantly affects the transient exchange of coherence between the system and its bath. We observe that single systems tend to retain coherence over time scales longer than that of the ensemble. We also compute a novel thermodynamic entanglement entropy that quantifies a thermodynamic driving force favoring system-bath entanglement.

Transition Metal-Based Ternary Catalysts Prepared By Electrodeposition for Hydrogen Evolution Reaction

To solve the global warming problem caused by indiscriminate use of fossil fuel, hydrogen production technology via water electrolysis is drawing attention. It is known that the Pt catalyst has been reported to be excellent for hydrogen evolution reaction (HER), which inhibits commercialization of water electrolysis due to its high price. For this reason, non-noble metal-based catalysts have been investigated to achieve cost-effectiveness with acceptable catalytic performance. It has recently been studied focusing on transition metals (Ni, Co, Mo, etc.) combined with non-metals (B, N, O, S, P, etc.) and reported indicating improved HER performance of transition metal borides and transition metal phosphides. In this study, nickel based complex containing phosphides and borides catalysts (Ni-P-B) were prepared on the carbon paper substrate using electrodeposition method. Phosphorous is reported to act as an active site due to its abundance of electrons and high electronegativity, and thus the catalytic performance of transition metal phosphides to HER increased with an increase in P ratio. On the other hand, boron has a different aspect. In transition metal borides, boron was expected to act as an active site due to its abundance and high electronegativity, but in practice the boron's electrons increase catalyst activity by donating electrons to the empty d-orbital. Nickel-based compounds containing phosphorus and boron (Ni–P–B) may be catalysts for HER, given the advantages of nickel phosphides and borides, but little research has been done on this. An experiment was conducted to increase the performance of the transition metal by adjusting the ratio of P and B in combination with the different properties of the transition metal phosphides and borides. Deposition parameters such as deposition potential/time and bath configuration were changed to control their morphology and composition. Their catalytic activity for HER was tested in half-cell measurement with the acidic electrolyte. Then the activity orders based on geometric current, specific activity, and mass activity were connected with the results from analysis on material properties. Furthermore, employing the optimized catalyst in cathode, the performance of proton exchange membrane water electrolyzer was tested.

Quantum energy transfer between a nonlinearly coupled bosonic bath and a fermionic chain: An exactly solvable model

The evolution of a quantum system towards thermal equilibrium is usually studied by approximate methods, which have their limits of validity and should be checked against analytically solvable models. In this paper, we propose an analytically solvable model to investigate the energy transfer between a bosonic bath and a fermionic chain which are nonlinearly-coupled to each other. The bosonic bath consists of an infinite collection of non-interacting bosonic modes, while the fermionic chain is represented by a chain of interacting fermions with nearest-neighbor interactions. We compare behaviors of the temperature-dependent energy current $J_{T}$ and temperature-independent energy current $J_{TI}$ for different bath configurations. With respect to the bath spectrum, $J_{T}$ decays exponentially for Lorentz-Drude type bath, which is the same as the conventional approximations. On the other hand, the decay rate is $1/t^{3}$ for Ohmic type and $1/t$ for white noise, which doesn't have conventional counterparts. For the temperature-independent current $J_{TI}$, the decay rate is divergent for the Lorentz-Drude type bath, $1/t^{4}$ for the Ohmic bath, and $1/t$ for the white noise. When further considering the dynamics of the fermionic chain, the current will be modulated based on the envelope from the bath. As an example, for a bosonic bath with Ohmic spectrum, when the fermionic chain is uniformly-coupled, we have $J_{T}\propto1/t^{6}$ and $J_{TI}\propto1/t^{3}$. Remarkably, for perfect state transfer (PST) couplings, there always exists an oscillating quantum energy current $J_{TI}$. Moreover, it is interesting that $J_{T}$ is proportional to $(N-1)^{1/2}$ at certain times for PST couplings under Lorentz-Drude or Ohmic bath.

Noncoalescent liquid metal droplets sustained on a magnetic field-circulated liquid metal bath surface

When exerting a rotating magnetic field on a liquid metal bath, the bath is driven to flow toward the magnetic field direction through the induced Lorentz force. Past a critical speed, a stable ring-shaped bath configuration is formed, and a droplet of the same liquid metal can persistently move without coalescence on the bath surface with a lubricating NaOH solution film between the two liquid metal bodies. The lubricating film allows the levitating droplet to rotate in the direction of the magnetic field. The magnetic field induced noncoalescence effect provides a noninvasive method to manipulate and study liquid metal droplet behavior on a soft substrate.

Polishing spherical BK7 workpieces with fiber-based tools

This work is a continuation of previously published work on the application of fiber-based tools in precision polishing of optical components. Previous publications mainly focused on understanding how fiber-based tools remove material and the potential of such tools in reducing existing midspatial frequency errors on planar samples. In this work, an exemplary tool consisting of nylon 6/6 fibers is used in a five-axis computerized numerically controlled machine tool to evaluate the tool’s ability to polish nonplanar BK7 components. The five-axis system has an inline slurry feed system which is found to produce higher material removal rates than the nonrecirculatory slurry bath configuration used in earlier polishing tests. Polishing results obtained on planar and spherical surfaces in the five-axis system show close agreement with that predicted via convolution. A finite element model of the fiber’s interaction with a concave surface shows that the calculated local pressure distribution reflects that observed experimentally, thus further supporting the predictable behavior of fiber-based tools.

Impact of Fill Ratio on Temperature Profile and Metal Bath Configuration in Electroslag Remelting Process With Vibrating Electrode

A transient three‐dimensional (3D) coupled model has been developed to investigate the impact of fill ratio on temperature distribution and metal bath configuration in electroslag remelting process with vibrating electrode. Based on the finite volume method, the continuity equation, Navier‐Stockes equations, and energy conservation equation are iteratively solved with full coupling of the Joule heating and Lorentz force. At the same time, the Joule heating and Lorentz force are calculated by the Maxwell's equations. The generation and dripping of metal droplets are simulated by the volume of fluid (VOF) approach. Moreover, an enthalpy‐porosity method is used to describe the metal solidification. The results show that varying fill ratio dramatically changes the temperature distribution of slag layer and metal bath configuration. While the fill ratio rises, both the highest temperature and time‐averaged temperature increase. Meanwhile, the high‐temperature region in the slag becomes larger and the temperature in the centre of slag layer becomes lower. The maximal metal bath depth reduces from 0.099 to 0.087 m while the fill ratio changes from 0.45 to 0.64.

Solving the Multi-site and Multi-orbital Dynamical Mean Field Theory Using Density Matrix Renormalization

We implement an efficient numerical method to calculate response functions of complex impurities based on the Density Matrix Renormalization Group (DMRG) and use it as the impurity-solver of the Dynamical Mean Field Theory (DMFT). This method uses the correction vector to obtain precise Green's functions on the real frequency axis at zero temperature. By using a self-consistent bath configuration with very low entanglement, we take full advantage of the DMRG to calculate dynamical response functions paving the way to treat large effective impurities such as those corresponding to multi-orbital interacting models and multi-site or multi-momenta clusters. This method leads to reliable calculations of non-local self energies at arbitrary dopings and interactions and at any energy scale.

One-Step Treatment of Spin–Orbit Coupling and Electron Correlation in Large Active Spaces

In this work we demonstrate that the heat bath configuration interaction (HCI) and its semistochastic extension can be used to treat relativistic effects and electron correlation on an equal footing in large active spaces to calculate the low energy spectrum of several systems including halogen group atoms (F, Cl, Br, I), coinage atoms (Cu, Au), and the neptunyl(VI) dioxide radical. This work demonstrates that despite a significant increase in the size of the Hilbert space due to spin symmetry breaking by the spin-orbit coupling terms, HCI retains the ability to discard large parts of the low importance Hilbert space to deliver converged absolute and relative energies. For instance, by using just over 107 determinants we get converged excitation energies for Au atom in an active space containing (150o,25e) which has over 1030 determinants. We also investigate the accuracy of five different two-component relativistic Hamiltonians in which different levels of approximations are made in deriving the one-electron and two-electrons Hamiltonians, ranging from Breit-Pauli (BP) to various flavors of exact two-component (X2C) theory. The relative accuracy of the different Hamiltonians are compared on systems that range in atomic number from first row atoms to actinides.

Review of Modeling and Simulation of Galvanizing Operations

Worldwide demand for galvanized steel products continues to grow for the assembly of automobile structures that are lighter and more resistant to impact, as well as for applications in the construction and domestic appliance industries. The technical challenges faced by these producers are the ability to coat a variety of low cost, high strength steels in developing a product with minimal surface defects, and reduced consumption of zinc and energy. The performance of the coating process depends on a thorough understanding of the reactions at the steel surface, the bath chemistry, the temperature variation in the bath, and the fluid dynamics of the coating operation. Operational parameters such as line speed, bath configuration, and immersed hardware all contribute to the variability of the process. Numerical simulations of this process have determined the spatial distribution of temperature and composition of the critical constituents in the zinc bath in transient turbulent flow conditions. This simulation is able to identify the rate of formation and the location of the intermetallic dross particles (dross) within the bath. The generation of dross at the surface of the bath is also simulated experimentally using a mixing system with variable agitation and with air or nitrogen gas streams. Industrial tests carried out to continuously monitor the variation of the temperature and the Al and Fe composition are able to confirm the variations determined by the numerical simulations, validating the use of numerical simulation as an important means of analyzing a complex metallurgical process.

Distribution of the position of a driven tracer in a hardcore lattice gas

.We study the position of a biased tracer particle (TP) in a bath of hardcore particles moving on a lattice of arbitrary dimension and in contact with a reservoir. Starting from the master equation satisfied by the joint probability of the TP position and the bath configuration and resorting to a mean-field-type approximation, we presented a computation of the fluctuations of the TP position in a previous publication (Bénichou et al 2013 Phys. Rev. E 87 032164). Counter-intuitively, on a one-dimensional lattice, the diffusion coefficient of the TP was shown to be a nonmonotonic function of the density of bath particles, and reaches a maximum for a nonzero value of the density. Here, we (i) give the details of this computation and offer a physical insight into the understanding of the nonmonotonicity of the diffusion coefficient; (ii) extend the mean-field-type approximation to decouple higher-order correlation functions, and obtain the evolution equation satisfied by the cumulant generating function of the position of the TP, valid in any space dimension. In the particular case of a one-dimensional lattice, we solve this equation and obtain the probability distribution of the TP position. We show that the position rescaled by its fluctuations is asymptotically distributed according to a Gaussian distribution in the long-time limit.

Entanglement dynamics of quantum oscillators nonlinearly coupled to thermal environments

We study the asymptotic entanglement of two quantum harmonic oscillators nonlinearly coupled to an environment. Coupling to independent baths and a common bath are investigated. Numerical results obtained using the Wangsness-Bloch-Redfield method are supplemented by analytical results in the rotating wave approximation. The asymptotic negativity as function of temperature, initial squeezing and coupling strength, is compared to results for systems with linear system-reservoir coupling. We find that due to the parity conserving nature of the coupling, the asymptotic entanglement is considerably more robust than for the linearly damped cases. In contrast to linearly damped systems, the asymptotic behavior of entanglement is similar for the two bath configurations in the nonlinearly damped case. This is due to the two-phonon system-bath exchange causing a supression of information exchange between the oscillators via the bath in the common bath configuration at low temperatures.

Improved Uniformity of Conformal Through-Hole Copper Electrodeposition by Revision of Plating Cell Configuration

Bath geometry and uniform electrolyte flow are the foundations of a uniform copper electrodeposition for printed circuit boards (PCBs) and electronic packaging applications. In order to achieve requirements for uniform electrodeposit thickness, a revised bath configuration was introduced to achieve copper electrodeposition of through holes (THs). Compared with Haring cell, uniformity of plated through hole (PTH) had been improved, especially for high aspect ratio TH. Furthermore, an electrochemical model for TH filling was constructed by multi-physical coupling technique. The model was utilized to investigate performances of copper electrodeposition, such as electrolyte flow field, resistance, current density distribution and electrodeposit thickness. The results indicated that for high aspect ratio TH filling, electrolyte flow played an increasingly important role in uniform electroplating process, which was in good agreement with the experiments. Furthermore, the effects of forced convection on mass transport during copper electrodeposition were analyzed by electrochemical measurements. The re-optimized bath configuration is effective for uniform TH filling.

Effectiveness of Perturbation Theory Approaches for Computing Non-Condon Electron Transfer Dynamics in Condensed Phases

A description of electron transfer in condensed-phase media requires models that adequately describe the coupling of the electronic degrees of freedom to the surrounding nuclear coordinates. The spin-boson model has been the canonical model used to understand quantum dynamic processes in condensed-phase media over the last 25 years. Inherent in the standard model of a two-state quantum system coupled to a bosonic bath is the assumption that the Condon approximation is valid. In this context, the Condon approximation assumes that the bath configurations (coordinates) have no effect on the nonadiabatic coupling matrix element. While this is a useful model for electron transfer in small molecular systems, the validity of this approximation is less likely when large-scale motions of solvent molecules are strongly coupled to the electron transfer event, e.g., in molecular clamps and long-range electron transfer in biopolymers. In the present paper a general model for two-state electron transfer which allows for system-bath coupling in both the diagonal and off-diagonal (nonadiabatic) terms is studied. Time-dependent perturbation theory for this Hamiltonian is developed using a small polaron transformation. As noted in several recent studies, in a certain regime of parameter space, the relevant Hamiltonian admits an exact solution, termed the exactly solvable non-Condon Hamiltonian (or NCE). This limit, for which exact solutions are available, is used to benchmark the short- and long-time accuracy of various perturbative approaches. The validated perturbation equations are subsequently used to explore the role of non-Condon effects on electron transfer by systematically increasing the strength of the non-Condon coupling term from zero (i.e., the canonical spin-boson model) to the value that pertains to the exactly solvable non-Condon model (where non-Condon effects are significant).

Computational Study of the One and Two Dimensional Infrared Spectra of a Vibrational Mode Strongly Coupled to Its Environment: Beyond the Cumulant and Condon Approximations

The effect of the commonly employed Condon and second-order cumulant approximations on one- and two-dimensional infrared spectra is examined in the case of a vibrational mode which is strongly coupled to its environment. The analysis is performed within the context of the hydrogen stretch of a moderately strong hydrogen-bonded complex dissolved in a dipolar liquid. The IR spectra are calculated using an adiabatic mixed quantum-classical approach that treats the hydrogen quantum-mechanically, while the remaining degrees of freedom are treated classically. While the cumulant and Condon treatments are seen to produce extremely broad and rather structureless spectra, the non-Condon spectra are found to consist of several relatively narrow bands that can be traced back to subsets of bath configurations with large transition dipole moments. Thus, although the cumulant and Condon approximations can capture some general qualitative spectral trends and are able to reproduce some highly averaged quantities such as the photon-echo peak shift, they fail to reproduce many important features of the spectra. We show that the great sensitivity of the transition dipole moment to the bath configuration provides new means for decongesting the spectra, probing statistically unfavorable bath configurations, and obtaining unique information regarding the dynamics of individual subsets of bath configurations and of the rates of transitions between them.

Decoherence of a two-qubit system away from perfect symmetry

The decoherence of an asymmetric two-qubit system that is coupled via a variable interaction term to a common bath or two individual baths of harmonic oscillators is examined. The dissipative dynamics are evaluated using the Bloch-Redfield formalism. It is shown that the behavior of the decoherence effects is affected mostly by the symmetries between the qubit operator that is coupled to the environment and the temperature, whereas the differences between the two bath configurations are very small. Moreover, it is elaborated that small imperfections of the qubit parameters do not necessarily lead to a drastic enhancement of the decoherence rates.

Quantum vibrational state-dependent potentials for classical many-body simulations

In this paper, we present a method for constructing simple state-dependent many-body potentials for quantum vibrations in a classical bath. The approach is based on an adiabatic separation between high-frequency quantum vibrational modes of the solute and the lower frequency classical motion of the solvent, and on a first-order perturbation theory description of the dependence of the quantum energies on bath configuration. In the simplest realization of the method, the delocalized quantum probability density of the vibrational mode is approximated by a sum of two delta functions, with positions and weights chosen to represent the lowest three moments of the exact distribution. Thus, in the many-body description of the system, each atom describing the quantum vibration is represented by a pair of particles. These quantum particles are held in rigid relative position and interact with the bath via potentials the magnitudes of which are modified by the delta-function weights. The resulting approach allows the classical molecular dynamics of molecules in arbitrary quantum vibrational states to be simulated with a little more effort than a purely classical description. The applicability of the method is illustrated in many-body simulations of the dephasing of vibrational superposition states of I(2) in a cryogenic krypton matrix, yielding results in good agreement with experiment.

Optimization of affinity and ion-exchange chromatographic processes for the purification of proteins

This study documents several alternative approaches for the optimization of the ion-exchange and affinity chromatographic purification of proteins. In these approaches, the chromatographic process has been treated as a four-stage (adsorption, washing, elution, and regeneration) operation. Central to these investigations has been the elaboration of practical iterative procedures based on the use of theoretical models describing each of these stages. Predictions derived from these models have then been evaluated in terms of experimental data obtained using batch adsorption measurements in finite bath configurations and frontal breakthrough measurements with packed beds of different dimensions, containing nonporous and porous adsorbents of different selectivities and capacities for proteins. Commencing with the kinetic and distribution parameters derived from batch equilibrium measurements, the effect of the initial concentration of the target protein, the solid-liquid volume ratio, the superficial velocity and the column dimensions on the pressure drop, production rate, concentration profile, column utilization, and yield have been determined with packed beds. The potential of these iterative approaches to simplify the determination of key mass transfer and interaction parameters required for scale-up and economic optimization of chromatographic purifications of proteins has been examined using ion exchange, immobilized metal ion affinity, and triazine dye pseudo-affinity adsorbents of different selectivity and adsorption capacities.

Rising and falling film flows: Viewed from a first-order approximation

Abstract Steady flow of liquid film on a vertical plane solid surface that is either fixed, or rising in its own plane out of a bath of liquid, occurs in coating and various other applications. At low capillary number the free surface flow is nearly rectilinear and invites approximate analysis which reveals two families of solutions. In the first, the configuration of the bath meters rising film flow and the film thickness above. In the other, the thickness of a rising or falling film is controlled by conditions far above the bath; bath configuration affects film thickness only in a boundary layer-like region adjoining the bath. Between the families, a range of film thickness is found that cannot be realized in steady flow.