QOT, Quasiatomic Orbitals for Transport, is a suite of source codes written in Fortran and Matlab for modeling phase-coherent quantum transport in molecular- and nano-electronics using the electronic structure information obtained from first-principles density-functional theory (DFT) calculations. QOT is based on an efficient and accurate Green's function approach within the Landauer-Büttiker formalism using the recently developed ab initio nonorthogonal quasiatomic orbital basis-set, while these quasiatomic orbitals are efficiently and robustly transformed from Kohn-Sham wavefunctions subject to the maximal atomic-orbital similarity measure without iterative minimization. With this minimal basis-set, we can easily calculate electrical conductance using Green's function method, while keeping accuracy at the level of plane-wave DFT. Our approach has been validated in several studies of two-terminal electronic devices. In addition, conductance eigenchannel analysis and chemical bonding analysis enable us to have better understanding of microscopic mechanism of quantum transport.

Interfaces to plane-wave DFT codes: including VASP, Dacapo, and PWscf (PW in Quantum-Espresso package) using norm conserving and ultrasoft pseudopotentials and PAW method

QO module: construct highly localized QOs to reproduce electronic structure obtained from high-quality DFT planewave calculations up to a few eVs above the Fermi level; provide real-space QOs and their tight-binding Hamiltonian and overlap matrices, Mulliken and Lowdin charge analysis, (QO-projected) band structure and density of states, (energy/velocity/mass-resolved) Fermi surface for both spin-collinear and spin-noncollinear systems (with and without spin-orbit coupling)

NEGF module: calculate phase-coherent quantum transport using non-equilibrium Green's function method in the QO basis-set together with density of states and conductance eigenchannel analysis

GW/TDDFT module: calculate quasiparticle electronic structure and optical excitations using many-body perturbation theory in Hedin's GW approximation and time-dependent density-functional theory (TDDFT) in the QO basis-set (in development)

Visualization module: visualize volumetric data including QOs, conductance eigenchannels, and Fermi surface using VTK and POV-Ray, and atomistic structure using AtomEye and XCrySDen

Data flow: in the convenient NetCDF format

Xiaofeng Qian, Ju Li, and Sidney Yip, Calculating phase-coherent quantum transport in nanoelectronics with ab initio quasiatomic orbital basis set, Physical Review B 82, 195442 (2010) [ DOI | PDF ]

Xiaofeng Qian, Ju Li, Liang Qi, Cai-Zhuang Wang, Tzu-Liang Chan, Yong-Xin Yao, Kai-Ming Ho, and Sidney Yip, Quasiatomic orbitals for ab initio tight-binding analysis, Physical Review B 78, 245112 (2008)  [ Website | DOI | PDF ]

T.-L. Chan, Y. X. Yao, C. Z. Wang, W. C. Lu, J. Li, X. F. Qian, S. Yip, and K. M. Ho, Highly localized quasiatomic minimal basis orbitals for Mo from ab initio calculations, Physical Review B 76, 205119 (2007)  [ DOI ]

Wen-Cai Lu, Cai-Zhuang Wang, Tzu-Liang Chan, Klaus Ruedenberg and Kai-Ming Ho, Representation of electronic structures in crystals in terms of highly localized quasiatomic minimal basis orbitals, Physical Review B 70, 041101(R) (2004)  [ DOI ]