The local structure organization and dynamics in lithium borate ionic liquids using molecular dynamics simulation

Despite significant progress in the development of lithium-ion batteries, the majority still rely on electrolytes based on organic solvents. However, single-ion conducting electrolytes offer a promising alternative by mitigating overpotential at the electrode and, thus, increasing the device's lifespan. In a recent study, Guzman-Gonzalez et al. (Adv. Energy Mater., 2022, 2202974) presented a novel approach to designing a new class of lithium ionic liquids, based on tetracoordinated boron atom with oligoethylene glycol groups and different fluorinated electron-withdrawing groups. To gain insights into the structural and dynamic aspects underlying the high ionic conductivity of these electrolytes, molecular dynamics simulations were employed. Our results establish a relationship between the variation in ionic conductivity and the extent of uncorrelated motion among the counterions. This phenomenon was explained by differences in the rate of ion coordination dynamics

The effect of off-diagonal density matrix in DFT+DMFT for Li2_2MnO3_3

Li$_2$MnO$_3$ has garnered much attention as one of the new-generation battery material, due to the high capacity and low cost. In the present work, we performed density functional theory (DFT)+$U$ and dynamical mean field theory (DMFT) calculations with continuous time quantum Monte Carlo impurity solver to study the electronic properties of Li$_2$MnO$_3$. Due to the nature of monoclinic $C2/m$ symmetry, the off-diagonal terms in the $d$-orbital block Hamiltonian (and $d$-orbital density matrix) are large, which results the large suppression of the energy gap due to the underestimation of the crystal-field splitting. We diagonalize the Mn $d$ block in the full $p-d$ Hamiltonian by applying unitary rotation matrix, and obtained an energy gap of 0.8 eV, although it is still smaller than the experimental gap of 2.1 eV even with the large $U$. In the $p$-$d$ model, a small double counting energy is essential to reduce the $p$-$d$ hybridization, thus to obtain the experimental gap. We show that the low-energy ($d$-only basis) model is efficient to study the electronic structure of Li$_2$MnO$_3$, since the Wannier basis is the hybridized state of Mn $d$ and O $p$ orbitals. These results suggest the correct way to investigate the low-symmetry materials using DFT+ DMFT method and to our knowledge, there is no systematic study of the effect of the off-diagonal terms so far. We also find that the antiferromagnetic ground state $\Gamma_{2u}$ is stable with $U \leq 2$ within DFT+$U$, which is much smaller than widely used $U$=5 eV.Comment: 8 pages, 8 figure

Lateral spin-orbit interaction and spin polarization in quantum point contacts

We study ballistic transport through semiconductor quantum point contact systems under different confinement geometries and applied fields. In particular, we investigate how the {\em lateral} spin-orbit coupling, introduced by asymmetric lateral confinement potentials, affects the spin polarization of the current. We find that even in the absence of external magnetic fields, a variable {\em non-zero spin polarization} can be obtained by controlling the asymmetric shape of the confinement potential. These results suggest a new approach to produce spin polarized electron sources and we study the dependence of this phenomenon on structural parameters and applied magnetic fields. This asymmetry-induced polarization provides also a plausible explanation of our recent observations of a 0.5 conductance plateau (in units of $2e^2/h$) in quantum point contacts made on InAs quantum-well structures. Although our estimates of the required spin-orbit interaction strength in these systems do not support this explanation, they likely play a role in the effects enhanced by electron-electron interactions.Comment: Summited to PRB (2009

Delocalized polaron and Burstein-Moss shift induced by Li in α\alpha-V2O5\textrm{V}_{2}\textrm{O}_{5}: DFT+DMFT study

We performed density functional theory (DFT)+$U$ and dynamical mean field theory (DMFT) calculations with continuous time quantum Monte Carlo impurity solver to investigate the electronic properties of V$_2$O$_5$ and Li$_x$V$_2$O$_5$ ($x$ = 0.125 and 0.25). Pristine V$_2$O$_5$ is a charge-transfer insulator with strong O $p$-V $d$ hybridization, and exhibits a large band gap ($E_{\textrm{gap}}$) as well as non-zero conduction band (CB) gap. We show that the band gap, the number of $d$ electrons of vanadium, $N_d$, and conduction band (CB) gap for V$_2$O$_5$ obtained from our DMFT calculations are in excellent agreement with the experimental values. While the DFT+$U$ approach replicates the experimental band gap, it overestimates the value of $N_d$ and underestimates the CB gap. In the presence of low Li doping, the electronic properties of V$_2$O$_5$ are mainly driven by a polaronic mechanism, the electron spin resonance and electron nuclear double resonance spectroscopies observed the coexistence of free and bound polarons. Notably, our DMFT results identify both polaron types, with the bound polaron being energetically preferred, while DFT+$U$ method predicts only the free polaron. Our DMFT analysis also reveals that increased Li doping leads to electron filling in the conduction band, shifting the Fermi level, this result consistent with the observed Burstein-Moss shift upon enhanced Li doping and we thus demonstrate that the DFT+DMFT approach can be used for accurate and realistic description of strongly correlated materials.Comment: 12 pages, 13 figure

Multi-UAV trajectory planning problem using the difference of convex function programming

The trajectory planning problem for a swarm of multiple UAVs is known as a challenging nonconvex optimization problem, particularly due to a large number of collision avoidance constraints required for individual pairs of UAVs in the swarm. In this paper, we tackle this nonconvexity by leveraging the difference of convex function (DC) programming. We introduce the slack variables to relax and reformulate the collision avoidance conditions and employ the penalty function term to equivalently convert the problem into a DC form. Consequently, we construct a penalty DC algorithm in which we sequentially solve a set of convex optimization problems obtained by linearizing the collision avoidance constraint. The algorithm iteratively tightens the safety condition and reduces the objective cost of the planning problem and the additional penalty term. Numerical results demonstrate the effectiveness of the proposed approach in planning a large number of UAVs in congested space.Comment: This paper has been accepted for presentation at the 62nd IEEE Conference on Decision and Control (CDC 2023

Interpretation Bias Characterizes Trait Rumination

Background and Objectives: Rumination, a maladaptive cognitive style of responding to negative mood, is thought to be maintained by a variety of cognitive biases. However, it is unknown whether rumination is characterized by interpretation biases. Methods: Two experiments examined the link between rumination and interpretation biases, revealed in lexical-decision tasks (LDT). A homograph with both benign and ruminative or otherwise negative meaning was presented on each trial and followed by a letter string, to which participants responded by judging whether it was a word or a non-word. Letter strings were nonwords or words related or unrelated to one meaning of the homograph. Results: In both experiments, faster latencies to respond to targets related to the ruminative meaning of the homographs were produced by students with higher scores on self-report measures of rumination. Moreover, these biases were associated with both brooding, the maladaptive form of rumination, and reflection, the more adaptive component. No measure of rumination was significantly correlated with general biases toward negative meaning (Experiment 1) or with threatening interpretations of homographs (Experiment 2). Limitations: The paucity of available rumination-related homographs dictated the use of nonfully randomized stimuli presentation (Experiment 1) or the use of only one set of the meanings associated with the homographs (Experiment 2). Conclusions: Rumination is associated with a tendency to interpret ambiguous information in a rumination-consistent manner. This tendency may exacerbate ruminative thinking and can possibly be a target for future intervention

Spatial correlations in chaotic nanoscale systems with spin-orbit coupling

We investigate the statistical properties of wave functions in chaotic nanostructures with spin-orbit coupling (SOC), focussing in particular on spatial correlations of eigenfunctions. Numerical results from a microscopic model are compared with results from random matrix theory in the crossover from the gaussian orthogonal to the gaussian symplectic ensembles (with increasing SOC); one- and two-point distribution functions were computed to understand the properties of eigenfunctions in this crossover. It is found that correlations of wave function amplitudes are suppressed with SOC; nevertheless, eigenfunction correlations play a more important role in the two-point distribution function(s), compared to the case with vanishing SOC. Experimental consequences of our results are discussed.Comment: Submitted to PR

A quantitative study of spin-flip co-tunneling transport in a quantum dot

We report detailed transport measurements in a quantum dot in a spin-flip co-tunneling regime, and a quantitative comparison of the data to microscopic theory. The quantum dot is fabricated by lateral gating of a GaAs/AlGaAs heterostructure, and the conductance is measured in the presence of an in-plane Zeeman field. We focus on the ratio of the nonlinear conductance values at bias voltages exceeding the Zeeman threshold, a regime that permits a spin flip on the dot, to those below the Zeeman threshold, when the spin flip on the dot is energetically forbidden. The data obtained in three different odd-occupation dot states show good quantitative agreement with the theory with no adjustable parameters. We also compare the theoretical results to the predictions of a phenomenological form used previously for the analysis of non-linear co-tunneling conductance, specifically the determination of the heterostructure g-factor, and find good agreement between the two.Comment: 5 pages, 5 figure