Browsing by Subject "Charge density wave"

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    Hubbard model In Square Lattices: A Mean-field Hartree-fock Approach
    (2005) Yönaç, Muhammed
    This thesis is mainly an effort to reproduce the well-known results that HartreeFock approximation gives for the Hubbard Model in two dimensions. As the area of application magnetic phases in the finite-size square lattices was chosen. The reason of choosing this particular area is that in the sources we went through mean-field theory was used only for examining the magnetic phases for rectangular density of state not for the actual density of states of a square lattice. We used the mean-field Hartree-Fock approximation and obtained the phase diagrams for the paramagnetic, ferromagnetic, charge density wave (CDW) and spin density wave (SDW) phases. The antiferromagnetic phase was found to be a special kind of the SDW phase. The hamiltonians used for the ferromagnetic and paramagnetic cases were identical. However because of the non-diagonal correlations present in the system the CDW and SDW hamiltonian was different.
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    Stable monolayer of the RuO2 structure by the Peierls distortion
    (Taylor & Francis, 2019-10-29) Ersan, Fatih; Özaydın, H. D.; Üzengi Aktürk, O.
    In this paper, we presented a stable two-dimensional ruthenium dioxide monolayer by using first-principles calculations within density functional theory. In contrast to ordinary hexagonal and octahedral structures of metal dichalcogenides, RuO2 is stable in the distorted phase of the structure as a result of occurring charge density wave. A comprehensive analysis including the calculation of vibration frequencies, mechanical properties, and ab initio molecular dynamics at 300 K affirms that RuO2 monolayer structure is stable dynamically and thermally and convenient for applications at room temperature. We also investigated the electronic and optical properties of RuO2 and it is found that RuO2 has of 0.74 eV band gap which is in the infrared region and very suitable for infrared detectors.