arXiv subjects

Xi-Jing Ning

Publications and source records attributed to Xi-Jing Ning.

14 recordsLinked to original sources

arXiv2024

Equation of state of rhenium under high temperatures and pressures predicted by ensemble theory

The high-temperature and high-pressure equations of states (EOSs) of rhenium up to 3000 K and 900 GPa are predicted by a recently developed method in the framework of statistical ensemble theory with \textit{ab initio} computational precision. The predicted isothermal EOSs are generally consistent with semi-empirical calculations below 150 GPa and 3000 K. Especially, the predicted isobaric EOS at one atmosphere is in good agreement with previous experiments. Moreover, the bulk modulus obtained in this work is closer to the experimental measurements than other theoretical works. Based on our calculations, the disputes between previous experiments are analyzed, and it is expected that the EOSs predicted under extreme conditions might be verified in future experiments.

cond-mat.mtrl-sci↗

arXiv2022

Equation of state for tungsten predicted by ensemble theory

Equation of state (EOS) for bcc tungsten at 300 K (or 3000 K) up to 1000 GPa (or 300 GPa) was predicted for the first time by solving the partition function via a direct integral approach (DIA) with ab initio calculations of the atoms' interactions. Compared with available experiments under static compressions up to 150 GPa (or 35 GPa) for room temperature (or 1673 K), all the calculated results are within the experimental uncertainty achieved very recently. Furthermore, the same procedure was performed to investigate the shock wave experiments on the EOS up to 400 GPa and 10000 K, and the calculated average pressure deviates the experimental measurements by only 2.0%. These facts suggest that the other calculated results of DIA for the EOS are reliable, and DIA as a universal method without any artificial parameters could be widely applied to predict EOS of various materials under various conditions.

cond-mat.mtrl-sci↗

arXiv2022

Pressure-induced structural phase transition of vanadium: A revisit from the perspective of ensemble theory

For realistic crystals, the free energy strictly formulated in ensemble theory can hardly be obtained because of the difficulty in solving the high-dimension integral of the partition function, the dilemma of which makes it even a doubt if the rigorous ensemble theory is applicable to phase transitions of condensed matters. In the present work, the partition function of crystal vanadium under compression up to $320$ GPa at room temperature is solved by an approach developed very recently, and the derived equation of state is in a good agreement with all the experimental measurements, especially the latest one covering the widest pressure range up to $300$ GPa. Furthermore, the derived Gibbs free energy proves the very argument to understand most of the experiments reported in the past decade on the pressure-induced phase transition, and, especially, a novel phase transition sequence concerning three different phases observed very recently and the measured angles of two phases agree with our theoretical results excellently.

cond-mat.stat-mech↗

arXiv2021

Photovoltaic Self-Powered Gas Sensing: A Review

The self-powered sensing system could harness ambient energy to power the sensor without the need for external electrical energy. Recently, the concept of photovoltaic (PV) self-powered gas sensing has aroused wider attentions due to room-temperature operation, low power consumption, small size and potential applications. The PV self-powered gas sensors integrate the photovoltaic effects and the gas sensing function into a single chip, which could truly achieve the goal of zero power consumption for an independent gas sensing device. As an emerging concept, the PV self-powered gas sensing has been achieved by using different strategies, including integrated gas sensor and solar cell, integrated light filter and solar cell, gas-sensitive heterojunction photovoltaics, and gas-sensitive lateral photovoltaics, respectively. The purpose of this review is to summarize recent advances of PV self-powered gas sensing and also remark on the directions for future research in this topic.

physics.app-ph↗

arXiv2019

Solution to the key problem of statistical physics -- calculations of partition function of many-body systems

The key problem of statistical physics standing over one hundred years is how to exactly calculate the partition function (or free energy) of many-body interaction systems, which severely hinders application of the theory for realistic systems. Here we present a novel approach that works at least four orders faster than state-of-the-art algorithms to the problem and can be applied to predict thermal properties of large molecules or macroscopic condensed matters via \emph{ab initio} calculations.The method was demonstrated by C$_{60}$ molecules, solid and liquid copper (up to $\sim 600$GPa), solid argon, graphene and silicene on substrate, and the derived internal energy or pressure is in a good agreement with the results of vast molecular dynamics simulations in a temperature range up to $2500$K, achieving a precision at least one order higher than previous methods. And, for the first time, the realistic isochoric equation of state for solid argon was reproduced directly from the partition function.

cond-mat.stat-mech↗

arXiv2019

What retards the response of graphene based gaseous sensor

Graphene based sensor to gas molecules should be ultrasensitive and ultrafast because of the single-atomic thickness of graphene, while the response is not fast. Usually, the measured response time for many molecules, such as CO, NH3, SO2, CO2 and NO2 and so on, is on the scale of minutes or longer. In the present work, we found via \emph{ab initio} calculations there exists a potential barrier larger than 0.7 eV that hinders the gas molecule to land directly at the defective sites of graphene and retards the response. An efficient approach to the problem is suggested as modifying the graphene sheet with other molecules to reduce the potential barrier and was demonstrated by a graphene sheet modified by Fe2O3 molecules that shows fast response to H2S molecule, and the calculated response time is close to the measured one, 500 $μ$s.

cond-mat.mes-hall↗

arXiv2019

Comparison of two efficient methods for calculating partition functions

In the long-time pursuit of the solution to calculate the partition function (or free energy) of condensed matter, Monte-Carlo-based nested sampling should be the state-of-the-art method, and very recently, we established a direct integral approach that works at least four orders faster. In present work, the above two methods were applied to solid argon at temperatures up to $300$K, and the derived internal energy and pressure were compared with the molecular dynamics simulation as well as experimental measurements, showing that the calculation precision of our approach is about 10 times higher than that of the nested sampling method.

cond-mat.stat-mech↗

arXiv2019

Calculating the free energy of 2D materials on substrates

A method was developed to calculate the free energy of 2D materials on substrates and was demonstrated by the system of graphene and γ-graphyne on copper substrate. The method works at least 3 orders faster than state-of-the-art algorithms, and the accuracy was tested by molecular dynamics simulations, showing that the precision for calculations of the internal energy achieves up to 0.03% in a temperature range from 100 to 1300K. As expected, the calculated the free energy of a graphene sheet on Cu (111) or Ni (111) surface in a temperature range up to 3000K is always smaller than the one of a γ-graphyne sheet with the same number of C atoms, which is consistent with the fact that growth of graphene on the substrates is much easier than γ-graphyne.

cond-mat.mtrl-sci↗

arXiv2013

Predicting the growth rate of helium bubbles in metal tritide

Helium bubbles nucleation and growth in metals or metal tritide is a long-standing problem attracting considerable attention in nuclear industry but the mechanism remains indistinct and predicting the growth rate of helium bubble is inexistence still up to new. Here, the rate of helium bubbles nucleation and growth in metal tritide is developed based on a dynamical model, which describes the diameter of helium bubbles increasing linearly as t**(1/3) in titanium tritide at room temperature, agreeing quite well with the experimental phenomenon. The way of reducing storage temperature from 300 to 225 K or increasing the helium atoms diffusion barrier from 0.81 to 1.1 eV can effectively restrain bubbles growth and prolong lifetime of titanium tritide more than 4 times, which provides a useful reference to relevant experiment exploration and applications. This model also can be used to predict lifetime of new tritium-storage materials and plasma facing materials in nuclear industry.

cond-mat.mtrl-sci↗

arXiv2013

If graphynes turn into graphene: the thermal stability study

The thermal stability of $α$-, $β$-, 6,6,12-graphyne and graphdiyne was studied by a statistic model, which was seriously tested by classical molecular dynamics simulations. By first-principles calculations of related potential energy curves, the model predicts that all the lifetime of free-standing single layer graphynes considered is more than 10$^{44}$ years at room temperature. When the temperature gets up to 1000 K, they are still very stable, but quickly turn into graphene if the temperature is about 2000 K

cond-mat.mes-hall↗

arXiv2013

Tuning the Conductance of Monatomic Carbon Chain

Ab initio calculations show that the conductance of short monatomic carbon chain can be dramatically modified by adhering a single H, N, or O atom to the chain. For example, the conductance of the pristine chain gets about two orders of magnitude smaller if an H atom is adhered to the chain. By a statistical model, the structure of the carbon chain with the single atom adhered is found to be quite stable at room temperature, indicating that the method can be used to tune the conductance of monatomic carbon chain.

cond-mat.mes-hall↗

arXiv2013

A scheme for realizing continuously tunable spectrum in the visible light region based on monatomic carbon chains

We propose a scheme for realizing the continuously tunable spectrum based on monatomic carbon chains. By hybrid density functional calculations, we first show that the direct band gap of monatomic carbon chains change continuously from 1.58 to 3.8 eV as strain is applied from -5 to 10% to the chain, with separated Van Hove singularity peaks enhanced. To realize this tunability, a realistic stretching device is proposed by contacting the chain with graphene sheets, which can apply up to 9% elongation to the chain, yielding tunable light-emitting wavelengths from 345 to 561 nm.

cond-mat.mes-hall↗

arXiv2011

Crtierion of effective centre-of-mass method in Quantum Mechanics

In describing the motion of atoms and clusters, we face with choosing quantum mechanics or classical mechanics under different conditions. In principle, there exist two criteria for this choice, but they do contradict in some cases though they are in agreement for other cases. Actually, this problem is closely related with the effective centre-of-mass method, the underlying application of quantum mechanics. It is shown that quantum mechanics must be selected for particle's motion when the de Broglie wave length of the mass centre is larger than the particle size, and in such case the effective centre-of-mass can be used in Quantum Mechanics. In order to test this conclusion, an easy-manufactured experiment is suggested.

quant-ph↗

arXiv2008

Coherent population trapping in a dressed two-level atom via a bichromatic field

We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed as dressed-state coherent population trapping. Such effect can be viewed as a new doorknob to manipulate a two-level system via its control over dressed-state populations. Application of this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion are discussed to demonstrate such controllability.

physics.optics↗