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A new model dielectric function for loss functions and electron damping.

ABSTRACT: Trends in the zeroth frequency moment of the imaginary part of the dielectric function are studied for a wide range of metals, semiconductors and insulators. These results are combined with estimates for the inverse-first moment (related by Kramers-Kronig relations to the static dielectric function) and knowledge of the first moment from the f-sum rule. Matching all three moments allows for construction of a model dielectric function that reasonably predicts the loss function at different values of momentum and lifetime damping effects on occupied and unoccupied electron states. This is demonstrated by comparing model results and results of detailed, first-principles calculations.

SUBMITTER: Shirley EL

PROVIDER: S-EPMC8370026 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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A new model dielectric function for loss functions and electron damping.

Shirley Eric L EL

Radiation physics and chemistry (Oxford, England : 1993) 20200201

Trends in the zeroth frequency moment of the imaginary part of the dielectric function are studied for a wide range of metals, semiconductors and insulators. These results are combined with estimates for the inverse-first moment (related by Kramers-Kronig relations to the static dielectric function) and knowledge of the first moment from the f-sum rule. Matching all three moments allows for construction of a model dielectric function that reasonably predicts the loss function at different values ...[more]

PMID: 34408339

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Project description:This groundbreaking study derives and tests several new dihedral torsion model potentials for constructing classical forcefields for atomistic simulations of materials. (1) The new angle-damped dihedral torsion (ADDT) model potential is preferred when neither contained equilibrium bond angle is linear (i.e., (θ eq ABC and θ eq BCD) ≠ 180°), at least one of the contained equilibrium bond angles is ≥ 130° (i.e., (θ eq ABC or θ eq BCD) ≥ 130°), and the dihedral torsion potential contains some odd-function contributions (i.e., U[ϕ] ≠ U[-ϕ]). (2) The new angle-damped cosine only (ADCO) model potential is preferred when neither contained equilibrium bond angle is linear (i.e., (θ eq ABC and θ eq BCD) ≠180°), at least one of the contained equilibrium bond angles is ≥ 130° (i.e., (θ eq ABC or θ eq BCD) ≥ 130°), and the dihedral torsion potential contains no odd-function contributions (i.e., U[ϕ] = U[-ϕ]). (3) The new constant amplitude dihedral torsion (CADT) model potential is preferred when neither contained equilibrium bond angle is linear (i.e., (θ eq ABC and θ eq BCD) ≠ 180°), both contained equilibrium bond angles are <130° (i.e., (θ eq ABC and θ eq BCD) < 130°), and the dihedral torsion potential contains some odd-function contributions (i.e., U[ϕ] ≠ U[-ϕ]). (4) The constant amplitude cosine only (CACO) model potential is preferred when neither contained equilibrium bond angle is linear (i.e., (θ eq ABC and θ eq BCD) ≠180°), both contained equilibrium bond angles are <130° (i.e., (θ eq ABC and θ eq BCD) <130°), and the dihedral torsion potential contains no odd-function contributions (i.e., U[ϕ] = U[-ϕ]). (5) The new angle-damped linear dihedral (ADLD) model potential is preferred when at least one contained equilibrium bond angle is linear (i.e., (θ eq ABC or θ eq BCD) = 180°). Most importantly, this article derives combined angle-dihedral coordinate branch equivalency conditions and angle-damping factors that ensure the angle-damped torsion model potentials (e.g., ADDT, ADCO, and ADLD) are mathematically consistent and continuously differentiable even as at least one contained bond angle approaches linearity (i.e., as (θ ABC or θ BCD) → 180°). This article introduces the torsion offset potential (TOP). I show the TOP gives rise in some materials to the unusual physical phenomenon of slip torsion. For various molecules, extensive quantitative comparisons to high-level quantum chemistry calculations (e.g., CCSD) and experimental vibrational frequencies showed these new dihedral torsion model potentials perform superbly.

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A new model dielectric function for loss functions and electron damping.

Publications

A new model dielectric function for loss functions and electron damping.

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