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Showing 1 to 12 of 12 for “"Second Order Perturbation Theory"”.
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The Unreasonable Usefulness of Approximation by Linear Combination
… techniques are first applied to Hartree-Fock theory and then we attempt to design a linear scaling massively parallel electron correlation strategy based on second order perturbation theory.
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Double resonance Raman spectra of graphene : a full 2D calculation
… two-dimensional numerical calculation applying second-order perturbation theory. Tight binding expressions for both the TO phonon dispersion and the [pi] - [pi]* electronic bands are used, which are then fit to experimental or ab-initio results. We are able to reproduce the single-peak D mode of …
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An X- and Q-band electron paramagnetic resonance study of Mn2+ in a single crystal of NH4Cl0.9I0.1 in the temperature range 77-295 K
… set of initial parameters is then determined by second-order perturbation theory. These are then rigorously evaluated by a computer subroutine using the least-squares-fitting technique. The spectra obtained through angular variation of the crystal within the static magnetic field confirm the …
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Two-photon absorption in bulk semiconductors and quantum well structures and its applications
… wells, QWs, is presented, along with a new theory of ND 2PA in QWs is developed. Pulsed mid-IR detection of femtosecond pulses is investigated in two different semiconductor p-i-n photodiodes (GaAs and GaN). With the smaller gap materials having larger ND-2PA, it is observed that they have …
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A valence bond for several perturbations
A valence bond perturbation method is developed for the purpose of treating the pi electron spectra of molecules related to a parent conjugated hydrocarbon molecule. A spectral perturbation reflects the change in pi electron transition energy of the parent hydrocarbon as a result of heteroatom …
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Density-functional theory and beyond for organic electronic materials
… --, insbesondere mittels der Renormalized Second-order Perturbation Theory (rPT2). Der theoretische Zugang von rPT2 liegt in der Vielteilchenstörungstheorie und ist deshalb abhängig vom Startpunkt, also abhängig vom ungestörten Hamiltonoperator. Diese Arbeit zeigt durch umfangreiche …
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Two-particle level diagrammatic approaches for strongly correlated systems
… FLuctuation EXchange (FLEX) approximation or the Second Order Perturbation Theory (SOPT). We found that it provides a significant improvement of FLEX or SOPT and a satisfactory agreement with Quantum Monte Carlo results despite instabilities in the self-consistency at low temperatures and for …
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The phonon spectra of simple metals - higher order effects of the electron-ion interaction
… In the former, some terms of third and fourth order are retained, whereas in the latter, only terms of second order are retained, as has been customary in the past. An. expression for the bulk modulus is derived by studying the long-wavelength behavior of the phonon dynamical matrix in the …
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Effects of isotope doping on the phonon modes in graphene
… isotopic masses and for all wave-vectors using second order perturbation theory. We found that for natural concentrations of 13C, the contribution of isotopic scattering of optical modes is negligible when compared to the contribution from the electron-phonon interaction. Nevertheless, for …
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Multi-Configurational Investigation of Thermolytic Pathways of Highly Strained Ring Systems
… to be 39.7 kcal/mol at the MRMP/cc-pVTZ level of theory. The PES for ? bond rotation was explored in more detail for several trans pyrans and pyridines and also for trans cyclohexene and several of its functional isomers. The ground state geometries for each structure were computed using the …
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Theoretical study of Kondo effect and related transport properties in topological insulator systems
… surface states. First, we combine the second-order perturbation theory and the Boltzmann transport equation to calculate the magnetically induced resistivity in a topological insulator. Our result shows a non-perturbative behavior when conduction electrons and magnetic impurities' spins …
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Fundamental physics from observations of the early universe
… the fundamental questions in physics. The linear perturbation theory may not be accurate enough to interpret the observations from Planck and future CMB experiments. Second order effects may in particular be important in constraining the non-Gaussianity in the initial conditions of the Universe. …