Ab initio molecular simulations with numeric atom-centered orbitals

Abstract

We describe a complete set of algorithms for ab initio molecular simulations based on numerically tabulated atom-centered orbitals (NAOs) to capture a wide range of molecular and materials properties from quantum-mechanical first principles. The full algorithmic framework described here is embodied in the Fritz Haber Institute "ab initio molecular simulations" (FHI-aims) computer program package. Its comprehensive description should be relevant to any other first-principles implementation based on NAOs. The focus here is on density-functional theory (DFT) in the local and semilocal (generalized gradient) approximations, but an extension to hybrid functionals, Hartree–Fock theory, and MP2/GW electron self-energies for total energies and excited states is possible within the same underlying algorithms. An all-electron/full-potential treatment that is both computationally efficient and accurate is achieved for periodic and cluster geometries on equal footing, including relaxation and ab initio molecular dynamics. We demonstrate the construction of transferable, hierarchical basis sets, allowing the calculation to range from qualitative tight-binding like accuracy to meV-level total energy convergence with the basis set. Since all basis functions are strictly localized, the otherwise computationally dominant grid-based operations scale as O(N) with system size N. Together with a scalar-relativistic treatment, the basis sets provide access to all elements from light to heavy. Both low-communication parallelization of all real-space grid based algorithms and a ScaLapack-based, customized handling of the linear algebra for all matrix operations are possible, guaranteeing efficient scaling (CPU time and memory) up to massively parallel computer systems with thousands of CPUs

Evidence for photogenerated intermediate hole polarons in ZnO

“…The electron or hole energy is renormalized by the electronphonon interaction. Polaron BEs were calculated from first principles using the Fritz Haber Institute ab initio molecular simulations (FHI-aims) code 21 and the Heyd-Scuseria-Ernzerhof hybrid density-functional (HSE06) 6,13 , see computational methods. The computed BEs are 33 meV for the large electron and 81 meV for the large hole polaron.…”

First‐Principles Modeling of Point Defects and Complexes in Thin‐Film Solar‐Cell Absorber CuInSe2

“…FHI-aims is an all-electron code in which electron wavefunctions are presented in the efficient basis of numerical atomic orbitals and in which the accuracy can be systematically improved by extending the basis set. [31] Thus, performing calculations by FHI-aims allows us also to verify whether the results depend on the basis set or the description of the core states. According to Figure 3 the absolute values of the formation energies and, consequently, also the charge transition levels, show only minor variations for supercells larger than 64 atoms, irrespective on the electronic-structure method used.…”

“…Here, in order to show the performance of even larger supercells, results for the 432-atom supercell are included. They are calculated using the FHI-aims code [31] and employing the HSE06 functional. FHI-aims is an all-electron code in which electron wavefunctions are presented in the efficient basis of numerical atomic orbitals and in which the accuracy can be systematically improved by extending the basis set.…”

Exploring the bonding of large hydrocarbons on noble metals: Diindoperylene on Cu(111), Ag(111), and Au(111)

“…The DFT + vdW surf method has been shown to yield remarkably accurate results for the structure and adsorption energies of xenon, benzene, and PTCDA on a variety of (111) metal surfaces. 7,26 The FHI-AIMS code 27 was employed for our DFT calculations. The repeated-slab method was used to model all systems with the vacuum gap set to 20Å.…”