arXiv subjects

Zhixin Qian

Publications and source records attributed to Zhixin Qian.

12 recordsLinked to original sources

arXiv2025

Impact of Radio Frequency Power on Columnar and Filamentary Modes in Atmospheric Pressure Very Low Frequency Plasma within Pores

The impact of radio frequency (RF) power on columnar and filamentary modes of very low frequency (VLF) plasma within pores is investigated in this work. The 12.5 kHz VLF discharge under various RF powers (13.56 MHz) was analyzed using optical photography and current-voltage measurements. Two-dimensional electron densities were derived using optical emission spectroscopy combined with collisional radiation modeling methods. It is found that RF power and very low frequency voltage (VVLF) significantly influence the plasma and its discharge modes within the 200 μm pore. Under low VVLF conditions, the plasma is more intense within the pore, and the discharge mode is columnar discharge. With increasing RF power, the reciprocal motion of electrons counteracts the local enhancement effect of columnar discharge, the discharge transforms into RF discharge, the pore is completely wrapped by the sheath, and the plasma inside is gradually quenched. Under high VVLF conditions, the electron density within the pore is low and the discharge mode is filamentary discharge. RF introduction reduces plasma intensity within the pores firstly. As RF power increases, more ion trapping in the pore increases the field strength distortion and enhances the plasma intensity inside the pore, this enhancement effects becomes more obvious with increasing RF power. In addition, the above effects were observed for all pore widths from 100 um to 1000 um. These findings provide key insights for controlling plasma in pores and offer new methodologies for plasma technology applications.

physics.plasm-ph↗

arXiv2016

Dielectric function with exact exchange contribution in the electron liquid. II. Analytical expression

The first-order, in terms of electron-interaction in the perturbation theory, of the proper linear response function $Π({\bf k}, ω)$ gives rise to the exchange-contribution to the dielectric function $ε({\bf k} , ω)$ in the electron liquid. Its imaginary part, $Im Π_1 ({\bf k}, ω)$, is calculated exactly. An analytical expression for $Im Π_1 ({\bf k}, ω)$ is derived which after refinement has a quite simple form.

cond-mat.str-el↗

arXiv2015

Static dielectric function with exact exchange contribution in the electron liquid

The exchange contribution, $Π_1 ({\bf k}, 0)$, to the static dielectric function in the electron liquid is evaluated exactly. Expression for it is derived analytically in terms of one quadrature. The expression, as presented in Eq. (3) in the Introduction, turns out to be very simple. A fully explicit expression (with no more integral in it) for $Π_1 ({\bf k}, 0)$ is further developed in terms of series. Equation (3) is proved to be equal to the expression obtained before under some mathematical assumption by Engel and Vosko, thus in the meanwhile putting the latter on a rigorous basis. The expansions of $Π_1 ({\bf k}, 0)$ at the wavectors of $k=0$, $k=2k_F$, and at limiting large $k$ are derived. The results all verify those obtained by Engel and Vosko.

cond-mat.str-el↗

arXiv2015

Asymptotic behavior of the Kohn-Sham exchange potential at a metal surface

The asymptotic structure of the Kohn-Sham exchange potential $v_x ({\bf r})$ in the classically forbidden region of a metal surface is investigated, together with that of the Slater exchange potential $V_x^S ({\bf r})$ and those of the approximate Krieger-Li-Iafrate $V_x^{KLI} ({\bf r})$ and Harbola-Sahni $W_x ({\bf r})$ exchange potentials. Particularly, the former is shown to have the form of $v_{x} (z \to \infty) = - α_x / z$ with $α_x$ a constant dependent only of bulk electron density. The same result in previous work is thus confirmed; in the meanwhile controversy raised recently gets resolved. The structure of the exchange hole $ρ_x ({\bf r}, {\bf r}')$ is examined, and the delocalization of it in the metal bulk when the electron is at large distance from the metal surface is demonstrated with analytical expressions. The asymptotic structures of $v_x ({\bf r})$, $V_x^S ({\bf r})$, $V_x^{KLI} ({\bf r})$, and $W_x ({\bf r})$ at a slab metal surface are also investigated. Particularly, $v_{x} (z \to \infty) = - 1/ z$ in the slab case. The distinction in this respect between the semi-infinite and the slab metal surfaces is elucidated.

cond-mat.str-el↗

arXiv2008

Bounds for the second and the third derivatives of the electron density at the nucleus

Lower bound for ${\bar ρ}''(0)$, the second derivative of the spherically averaged atomic electronic density at the nucleus, and upper bound for ${\bar ρ}'''(0)$, the third derivative, are obtained respectively. It is shown that, for the ground state, ${\bar ρ}''(0) \ge {10/3} Z^2 ρ(0)$ and ${\bar ρ}'''(0) \le -{14/3}Z^3 ρ(0)$ where $Z$ is the charge of the nucleus, and $ρ(0)$ is the electron density at the nucleus. Tighter bounds for ${\bar ρ}''(0)$ and ${\bar ρ}'''(0)$ are also reported which are valid for both the ground state and excited states. Explicit illustration with the example of one-electron atomic ions is given.

physics.atom-ph↗

arXiv2007

Asymptotic near nucleus structure of the electron-interaction potential in local effective potential theories

In local effective potential theories of electronic structure, the electron correlations due to the Pauli exclusion principle, Coulomb repulsion, and correlation-kinetic effects, are all incorporated in the local electron-interaction potential $v_{ee}({\bf r})$. In previous work, it has been shown that for spherically symmetric or sphericalized systems, the asymptotic near nucleus expansion of this potential is $v_{ee}(r) = v_{ee}(0) + βr + O(r^2)$, with $v_{ee}(0)$ being finite. By assuming that the Schrödinger and local effective potential theory wave functions are analytic near the nucleus of atoms, we prove the following via Quantal density functional theory (Q-DFT): (i) correlations due to the Pauli principle and Coulomb correlations do not contribute to the linear structure; (ii) these Pauli and Coulomb correlations contribute quadratically; (iii) the linear structure is {\em solely} due to correlation-kinetic effects, the contributions of these effects being determined analytically. We also derive by application of adiabatic coupling constant perturbation theory via Q-DFT (iv) the asymptotic near nucleus expansion of the Hohenberg-Kohn-Sham theory exchange $v_x({\bf r})$ and correlation $v_c({\bf r})$ potentials. These functions also approach the nucleus linearly with the linear term of $v_x({\bf r})$ being {\em solely} due to the lowest-order correlation kinetic effects, and the linear term of $v_c({\bf r})$ being due {\em solely} to the higher-order correlation kinetic contributions. The above conclusions are equally valid for systems of arbitrary symmetry, provided spherical averages of the properties are employed.

cond-mat.mtrl-sci↗

arXiv2007

Exchange and correlation near the nucleus in density functional theory

The near nucleus behavior of the exchange-correlation potential $v_{xc}({\bf r})$ in Hohenberg-Kohn-Sham density functional theory is investigated. It is shown that near the nucleus the linear term of $O(r)$ of the spherically averaged exchange-correlation potential ${\bar v}_{xc}(r)$ is nonzero, and that it arises purely from the difference between the kinetic energy density at the nucleus of the interacting system and the noninteracting Kohn-Sham system. An analytical expression for the linear term is derived. Similar results for the exchange $v_{x}({\bf r})$ and correlation $v_{c}({\bf r})$ potentials are also obtained separately. It is further pointed out that the linear term in $v_{xc}({\bf r})$ arising mainly from $v_{c}({\bf r})$ is rather small, and $v_{xc}({\bf r})$ therefore has a nearly quadratic structure near the nucleus. Implications of the results for the construction of the Kohn-Sham system are discussed with examples.

cond-mat.mtrl-sci↗

arXiv2006

Lifetime of a quasiparticle in an electron liquid. II

Inelastic lifetime of an electron quasiparticle in an electron liquid due to electron-electron interaction evaluated in previous work is calculated in an alternative way. Both the contributions of the "direct" and "exchange" processes are included. The results turn out to be exactly the same as those obtained previously, and hence confirm the latter. Derivation in the two-dimensional case is presented in great details due to its intricacies.

cond-mat.str-el↗

arXiv2005

The on-top pair-correlation density in the homogeneous electron liquid

The ladder theory, in which the Bethe-Goldstone equation for the effective potential between two scattering particles plays a central role, is well known for its satisfactory description of the short-range correlations in the homogeneous electron liquid. By solving exactly the Bethe-Goldstone equation in the limit of large transfer momentum between two scattering particles, we obtain accurate results for the on-top pair-correlation density $g(0)$, in both three dimensions and two dimensions. Furthermore, we prove, in general, the ladder theory satisfies the cusp condition for the pair-correlation density $g(r)$ at zero distance $r=0$.

cond-mat.str-el↗

arXiv2004

Lifetime of a quasiparticle in an electron liquid

We calculate the inelastic lifetime of an electron quasiparticle due to Coulomb interactions in an electron liquid at low (or zero) temperature in two and three spatial dimensions. The contribution of "exchange" processes is calculated analytically and is shown to be non-negligible even in the high-density limit in two dimensions. Exchange effects must therefore be taken into account in a quantitive comparison between theory and experiment. The derivation in the two-dimensional case is presented in detail in order to clarify the origin of the disagreements that exist among the results of previous calculations, even the ones that only took into account "direct" processes.

cond-mat.str-el↗

arXiv2004

Long wavelength behavior of the dynamical spin-resolved local-field factor in a two-dimensional electron liquid

The high frequency limits of the singular component $A(ω)$ of the small wavevector expansion of the longitudinal (L) and transverse (T) components of the spin-resolved exchange-correlation kernel tensor $f_{xc,σσ'}^{L,T}(q,ω)=-v(q)G_{σσ'}^{L,T}(q,ω)$ in a two-dimensional isotropic electron liquid with arbitrary spin polarization are studied. Here $G_{σσ'}^{L,T}(q,ω)$ is the spin-resolved local field factor, $v(q)$ is the Coulomb interaction in momentum space, and $σ$ denotes spin. Particularly, the real part of $A(ω)$ is found to be logarithmically divergent at large $ω$. the large wavevetor structure of the corresponding spin-resolved static structure factor is also established.

cond-mat.str-el↗

arXiv2001

Spin dynamics from time-dependent spin density-functional theory

We derive the spin-wave dynamics of a magnetic material from the time-dependent spin density functional theory in the linear response regime. The equation of motion for the magnetization includes, besides the static spin stiffness, a "Berry curvature" correction and a damping term. A gradient expansion scheme based on the homogeneous spin-polarized electron gas is proposed for the latter two quantities, and the first few coefficients of the expansion are calculated to second order in the Coulomb interaction.

cond-mat.mtrl-sci↗