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A. Valli, G. Gandus, D. Passerone, R. Stadler:
"Local orbitals for ab-initio and many-body simulations of nanoelectronic devices";
Poster: ElecMol 2021, Lyon; 29.11.2021 - 02.12.2021.

Atomic-like orbitals (AOs) within the LCAO formalism allow for computationally efficient calculations within density functional theory (DFT) although the numerical accuracy is limited by the quality of the basis set. At the same time, considering extensive basis sets poses a fundamental problem of physical interpretation of the results.
An alternative is to define local orbitals (LOs) which inherit the information of the local crystal field and have a natural physical interpretation. This can be done by subdiagonalization of the individual atomic blocks of the LCAO Hamiltonian. Keeping a suitable subset of relevant LOs is sufficient to provide an accurate description of the physics around the Fermi level, thus reducing to some extent the redundancy of the original basis set. Hence, LOs allow for, e.g., efficient DFT calculations of electronic structure and trasport properties without sacrificing the numerical accuracy. Such a reduced basis set is also useful for the definition of a ab-initio effective Hamiltonians to take into account many-body effects beyond DFT. We demonstrate the utility of LOs for materials with different chemical and physical properties, and we analyze strategies and perspectives for future applications.