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Stochastic many-body calculations of moiréstates in twisted bilayer graphene at high pressures

npj Computational Materials 2022年第1期8卷 89-98页

作者： Mariya Romanova Vojtěch Vlček Department of Chemistry and Biochemistry University of CaliforniaSanta BarbaraCA93106-9510USA

We introduce three developments within the stochastic many-body perturbation theory:efficient evaluation of off-diagonal self-energy terms,construction of Dyson orbitals,and stochastic constrained random phase approximation.The stochastic approaches readily handle systems with thousands of atoms.We use them to explore the electronic states of twisted bilayer graphene(tBLG)characterized by giant unit cells and correlated electronic states.We document the formation of electron localization under compression;weakly correlated states are merely shifted in energy.We demonstrate how to efficiently downfold the correlated subspace on a model Hamiltonian with a screened frequency-dependent two-body interaction.For the 6°tBLG system,the onsite interactions are between 200 and 300 meV under compression.The Dyson orbitals exhibit spatial distribution similar to the mean-field single-particle states.Under pressure,the electron-electron interactions increase in the localized states;however,the dynamical screening does not fully balance the dominant bare Coulomb interaction.

关键词： interaction twisted stochastic

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Dynamical downfolding for localized quantum states

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npj Computational Materials 2023年第1期9卷 1050-1058页

作者： Mariya Romanova Guorong Weng Arsineh Apelian Vojtěch Vlček Department of Chemistry and Biochemistry University of CaliforniaSanta BarbaraCA 93106-9510USA Department of Materials University of CaliforniaSanta BarbaraCA 93106-9510USA

We introduce an approach to treat localized correlated electronic states in the otherwise weakly correlated host medium.Here,the environment is dynamically downfolded on the correlated subspace.It is captured via renormalization of one and two quasiparticle interaction terms which are evaluated using many-body perturbation theory.We outline the strategy on how to take the dynamical effects into account by going beyond the static limit approximation.Further,we introduce an efficient stochastic implementation that enables treating the host environment with a large number of electrons at a minimal computational cost.For a small explicitly correlated subspace,the dynamical effects are critical.We demonstrate the methodology by reproducing optical excitations in the negatively charged NV center defect in diamond,that agree with experimental results.

关键词： theory subspace states

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