Time-dependent density functional theory of coupled electronic lattice motion in quasi-two-dimensional crystals

Nazarov, V. U.; Alharbi, Fahhad H.; Fisher, Timothy S.; Kais, Sabre

doi:10.1103/physrevb.89.195423

Cited by 14 publications

(17 citation statements)

References 33 publications

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“…Are they also plasmons at smaller q-s, or do they turn into single-particle transitions, although keep full similarity to their higher-q plasmon counterparts? To answer this question, we need to establish whether, although Re 2D ϵ does not cross zero at smaller wave-vectors, the features at the energy-loss function are due to Re 2D ϵ approaching zero, or they are due to peaks at Im 2D ϵ (see [17]). As can be seen in figure 2, middle panel, Im D 2 ε has a prominent non-dispersive (standing in place with the variation of q ∥ ) feature at ω ≈ 4 eV.…”

Section: Results Of Calculations and Discussionmentioning

confidence: 99%

“…This is, instead of considering a single layer (schematized in figure 1(a)), to artificially periodically replicate it in the z-direction ( figure 1(b)), and study the resulting 3D periodic system in place of the original single-layer one. It is, however, known [15][16][17] that the 3D dielectric function obtained in the super-cell geometry has nothing to do with that of a single-layer system of interest, unless a special procedure of extracting the 2D response from the 3D super-cell geometry calculation (i.e., the elimination of the spurious inter-layer interaction) is applied. In appendix A we give a detailed derivation of the expression for the density-response function χ of the single-layer system fromχ -the density-response function of the array system.…”

Section: Excitation Of Q2d System From the Super-cell Geometry Calculmentioning

confidence: 99%

“…Equation (A.3) corrects an error in equation (A.3) of[17]. However, all the formulas derived in[17] under the assumption of qa 1 ≪ , where a is the effective width of a layer, remain valid.…”

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confidence: 91%

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Electronic excitations in quasi-2D crystals: what theoretical quantities are relevant to experiment?

Nazarov

2015

New J. Phys.

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View the article online for updates and enhancements. Related contentToward a novel theoretical approach for determining the nature of electronic excitations in quasi-two-dimensional systems A Politano, G Chiarello and A Cupolillo -Low-energy dielectric screening in Pd and PdHx systems V M Silkin, V U Nazarov, I P Chernov et al.Acoustic plasmons in extrinsic freestanding graphene M Pisarra, A Sindona, P Riccardi et al. AbstractThe ab initio theory of electronic excitations in atomically thin (quasi-two-dimensional (Q2D)) crystals presents extra challenges in comparison to both the bulk and purely 2D cases. We argue that the conventionally used energy-loss function Im(where q , ϵ , and ω are the dielectric function, the momentum, and the energy transfer, respectively) is not, generally speaking, the suitable quantity for the interpretation of the electron-energy loss spectroscopy (EELS) in the Q2D case, and we construct different functions pertinent to the EELS experiments on Q2D crystals. Secondly, we emphasize the importance and develop a convenient procedure of the elimination of the spurious inter-layer interaction inherent to the use of the 3D super-cell method for the calculation of excitations in Q2D crystals. Thirdly, we resolve the existing controversy in the interpretation of the so-called π and π σ + excitations in monolayer graphene by demonstrating that both dispersive collective excitations (plasmons) and non-dispersive single-particle (inter-band) transitions fall in the same energy ranges, where they strongly influence each other.

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Section: Results Of Calculations and Discussionmentioning

confidence: 99%

Section: Excitation Of Q2d System From the Super-cell Geometry Calculmentioning

confidence: 99%

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Electronic excitations in quasi-2D crystals: what theoretical quantities are relevant to experiment?

Nazarov

2015

New J. Phys.

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“…Our time-dependent density-functional theory (TDDFT) calculation of the permittivity consists of two steps. Since Q2D systems lack periodicity in the z-direction, it is customary to use the super-cell method [12][13][14]. First, in the super-cell geometry, we calculate the density-response functionχ Gg,G ′ g ′ (q, ω; d) of an auxiliary 3D system comprised of an infinite periodic array of monolayers with the separation d between them, as is schematized in Fig.…”

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confidence: 99%

Negative static permittivity and violation of Kramers-Kronig relations in quasi-two-dimensional crystals

Nazarov

2015

Phys. Rev. B

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We investigate the wave-vector and frequency-dependent screening of the electric field in atomically thin (quasi-two-dimensional) crystals. For graphene and hexagonal boron nitride we find that, above a critical wave-vector qc, the static permittivity ε(q > qc, ω = 0) becomes negative and the Kramers-Kronig relations do not hold for ε(q > qc, ω). Thus, in quasi-two-dimensional crystals, we reveal the physical confirmation of a proposition put forward decades ago (Kirzhnits, 1976), allowing for the breakdown of Kramers-Kronig relations and for the negative static permittivity. In the vicinity of the critical wave-vector, we find a giant growth of the permittivity. Our results, obtained in the ab initio calculations using both the random-phase approximation and the adiabatic time-dependent local-density approximation, and further confirmed with a simple slab model, allow us to argue that the above properties, being exceptional in the three-dimensional case, are common to quasi-two-dimensional systems. The concept of causality plays one of the central roles in contemporary science [1]. It is well known that causality in the time-domain (the impossibility for an effect to precede the cause in time) leads to the analyticity of a causal response-function in a complex half-plane in the frequency-domain, which, in turn, leads to KramersKronig (KK) relations between the real and the imaginary parts of the response function [2].It must be, however, recognized that the causality assumes that the response-function is applied to a cause and it produces an effect. In the case of the longitudinal electric field in a translationally invarient or a periodic system, the definition of the permittivity ε(q, ω) reads φ tot (q, ω) = φ ext (q, ω)/ε(q, ω), where φ ext and φ tot are the scalar potentials of the externally applied and the total electric fields, respectively. Since the cause is φ ext and the effect is φ tot , not vice versa, this is 1/ε that is guaranteed to be causal, but not ε itself [3]. Accordingly, KK relations must be satisfied by 1/ε, but may or may not be satisfied by ε. For |q| > 0, this leaves ε(q, ω = 0) a freedom to be negative without violating the causality or destroying the stability of the system [4,5]. If this happens, then the inverse permittivity has zeros in the upper half of the complex ω-plane, making the permittivity itself a non-analytic function.In the three-dimensional world the realizations of such negative static permittivity are scarce and they mostly concern exotic non-crystalline systems [6][7][8][9][10]. In this work we show that, above a critical wave-vector q > q c in the first Brillouin zone, the permittivity ε(q, ω) of the quasi-two-dimensional (Q2D) systems of the monolayer graphene and boron nitride is negative in the static limit. Accordingly, KK relations for the permittivity do not hold in this case. The inverse permittivity, on the contrary, remains causal and does satisfy KK relations.We start by writing the permittivity of a Q2D crystal [11] (atomic units e 2 = = m e = 1 are use...

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“…Electronic energy decaying into ions by phonon creation is a process absent in TD-DFT and Ehrenfest dynamics; in this theory electrons and ions do not reach thermal equilibrium, rather ionic kinetic energy is transferred to electrons until all ions are at rest 10 , 19 – 21 . However these specific limitations of the theory are not relevant for our study because actual ion-electron thermalization occurs in time scales larger than those considered here; in fact the time scales explored in this study are so short that we do not allow target atoms to move during the simulations.…”

Section: Introductionmentioning

confidence: 99%

Stopping power beyond the adiabatic approximation

Caro

Correa

Artacho

et al. 2017

Sci Rep

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Energetic ions traveling in solids deposit energy in a variety of ways, being nuclear and electronic stopping the two avenues in which dissipation is usually treated. This separation between electrons and ions relies on the adiabatic approximation in which ions interact via forces derived from the instantaneous electronic ground state. In a more detailed view, in which non-adiabatic effects are explicitly considered, electronic excitations alter the atomic bonding, which translates into changes in the interatomic forces. In this work, we use time dependent density functional theory and forces derived from the equations of Ehrenfest dynamics that depend instantaneously on the time-dependent electronic density. With them we analyze how the inter-ionic forces are affected by electronic excitations in a model of a Ni projectile interacting with a Ni target, a metallic system with strong electronic stopping and shallow core level states. We find that the electronic excitations induce substantial modifications to the inter-ionic forces, which translate into nuclear stopping power well above the adiabatic prediction. In particular, we observe that most of the alteration of the adiabatic potential in early times comes from the ionization of the core levels of the target ions, not readily screened by the valence electrons.

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Time-dependent density functional theory of coupled electronic lattice motion in quasi-two-dimensional crystals

Cited by 14 publications

References 33 publications

Electronic excitations in quasi-2D crystals: what theoretical quantities are relevant to experiment?

Electronic excitations in quasi-2D crystals: what theoretical quantities are relevant to experiment?

Negative static permittivity and violation of Kramers-Kronig relations in quasi-two-dimensional crystals

Stopping power beyond the adiabatic approximation

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