arXiv subjects

Paul Ziesche

Publications and source records attributed to Paul Ziesche.

6 recordsLinked to original sources

arXiv2018

Screened exchange corrections to the random phase approximation from many-body perturbation theory

The random phase approximation (RPA) systematically overestimates the magnitude of the correlation energy and generally underestimates cohesive energies. This originates in part from the complete lack of exchange terms, which would otherwise cancel Pauli exclusion principle violating (EPV) contributions. The uncanceled EPV contributions also manifest themselves in form of an unphysical negative pair density of spin-parallel electrons close to electron-electron coalescence. We follow considerations of many-body perturbation theory to propose an exchange correction that corrects the largest set of EPV contributions while having the lowest possible computational complexity. The proposed method exchanges adjacent particle/hole pairs in the RPA diagrams, considerably improving the pair density of spin-parallel electrons close to coalescence in the uniform electron gas (UEG). The accuracy of the correlation energy is comparable to other variants of Second Order Screened Exchange (SOSEX) corrections although it is slightly more accurate for the spin-polarized UEG. Its computational complexity scales as $\mathcal O(N^5)$ or $\mathcal O(N^4)$ in orbital space or real space, respectively. Its memory requirement scales as $\mathcal O(N^2)$.

cond-mat.mtrl-sci↗

arXiv2009

The high-density electron gas: How its momentum distribution n(k) and its static structure factor S(q) are mutually related through the off-shell self-energy Sigma(k,omega)

It is shown {\it in detail how} the ground-state self-energy $Σ(k,ω)$ of the spin-unpolarized uniform electron gas (with the density parameter $r_s$) in its high-density limit $r_s\to 0 $ determines: the momentum distribution $n(k)$ through the Migdal formula, the kinetic energy $t$ from $n(k)$, the potential energy $v$ through the Galitskii-Migdal formula, the static structure factor $S(q)$ from $e=t+v$ by means of a Hellmann-Feynman functional derivative. The ring-diagram partial summation or random-phase approximation is extensively used and the results of Macke, Gell-Mann/Brueckner, Daniel/Vosko, Kulik, and Kimball are summarized in a coherent manner. There several identities were brought to the light.

cond-mat.str-el↗

arXiv2006

The on-shell self-energy of the uniform electron gas in its weak-correlation limit

The ring-diagram partial summation (or RPA) for the ground-state energy of the uniform electron gas (with the density parameter $r_s$) in its weak-correlation limit $r_s\to 0 $ is revisited. It is studied, which treatment of the self-energy $Σ(k,ω)$ is in agreement with the Hugenholtz-van Hove (Luttinger-Ward) theorem $μ-μ_0= Σ(k_{\rm F},μ)$ and which is not. The correlation part of the lhs h as the RPA asymptotics $a\ln r_s +a'+O(r_s)$ [in atomic units]. The use of renormalized RPA diagrams for the rhs yields the similar expression $a\ln r_s+a''+O(r_s)$ with the sum rule $a'= a''$ resulting from three sum rules for the components of $a'$ and $a''$. This includes in the second order of exchange the sum rule $μ_{2{\rm x}}=Σ_{2{\rm x}}$ [P. Ziesche, Ann. Phys. (Leipzig), 2006].

cond-mat.str-el↗

arXiv2002

Momentum distribution of the uniform electron gas: improved parametrization and exact limits of the cumulant expansion

The momentum distribution of the unpolarized uniform electron gas in its Fermi-liquid regime, n(k,r_s), with the momenta k measured in units of the Fermi wave number k_F and with the density parameter r_s, is constructed with the help of the convex Kulik function G(x). It is assumed that $n(0,r_s), n(1^\pm, r_s)$, the on-top pair density g(0,r_s) and the kinetic energy t(r_s) are known (respectively, from effective-potential calculations, from the solution of the Overhauser model, and from Quantum Monte Carlo calculations via the virial theorem). Information from the high- and the low-density limit, corresponding to the random-phase approximation and to the Wigner crystal limit, is used. The result is an accurate parametrization of n(k,r_s), which fulfills most of the known exact constraints. It is in agreement with the effective-potential calculation of Takada and Yasuhara [1991 {\it Phys. Rev.} B {\bf 44} 7879], is compatible with Quantum Monte Carlo data, and is valid in the density range $r_s \lesssim 12$. The corresponding cumulant expansions of the pair density and of the static structure factor are discussed, and some exact limits are derived.

cond-mat↗

arXiv2002

The Electron-Gas Pair Densities and their Normalization Sum Rules in Terms of Overhauser Geminals and Corresponding Scattering Phase Shifts

It is shown, how the normalization sum rules of the spin-parallel and spin-antiparallel pair densities of the homogeneous electron gas become sum rules for the scattering phase shifts of the Overhauser two-body wave functions (geminals), with which the pair densities have been successfully parametrized recently. These new sum rules relate two-body quantities to a one-body quantity, namely the asymptotics of the Overhauser geminals to the momentum distribution.

cond-mat.str-el↗

arXiv2000

Hellmann-Feynman theorem and fluctuation-correlation analysis of the Calogero-Sutherland model

Exploiting the results of the exact solution for the ground state of the one-dimensional spinless quantum gas of Fermions and impenetrable Bosons with the mu/x_{ij}^2 particle-particle interaction, the Hellmann-Feynman theorem yields mutually compensating divergences of both the kinetic and the interaction energy in the limiting case mu to -1/4. These divergences result from the peculiar behavior of both the momentum distribution (for large momenta) and the pair density (for small inter-particle separation). The available analytical pair densities for mu=-1/4, 0, and 2 allow to analyze particle-number fluctuations. They are suppressed by repulsive interaction (mu>0), enhanced by attraction (mu<0), and may therefore measure the kind and strength of correlation. Other recently proposed purely quantum-kinematical measures of the correlation strength arise from the small-separation behavior of the pair density or - for Fermions - from the non-idempotency of the momentum distribution and its large-momenta behavior. They are compared with each other and with reference-free, short-range correlation-measuring ratios of the kinetic and potential energies.

cond-mat.str-el↗