Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

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QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.

Multiwfn: a multifunctional wavefunction analyzer.

Recent extensions of the DMol3 local orbital density functional method for band structure calculations of insulating and metallic solids are described. Furthermore the method for calculating semilocal pseudopotential matrix elements and basis functions are detailed together with other unpublished parts of the methodology pertaining to gradient functionals and local orbital basis sets. The method is applied to calculations of the enthalpy of formation of a set of molecules and solids. We find that the present numerical localized basis sets yield improved results as compared to previous results for the same functionals. Enthalpies for the formation of H, N, O, F, Cl, and C, Si, S atoms from the thermodynamic reference states are calculated at the same level of theory. It is found that the performance in predicting molecular enthalpies of formation is markedly improved for the Perdew–Burke–Ernzerhof [Phys. Rev. Lett. 77, 3865 (1996)] functional.

From molecules to solids with the DMol3 approach

If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.

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Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials

X-ray absorption spectra: K-edges of 3d transition metals, L-edges of 3d and 4d metals, and M-edges of palladium

We have developed a method for calculating self-consistently the electronic structure around an impurity atom, or an impurity cluster, in a crystalline host. Our method is a Green-function matrix technique based on the linear muffin-tin orbital method in the atomic-spheres approximation. The calculation of the host Green function is extremely efficient and involves diagonalization of a small Hamiltonian matrix for the band structure and subsequent Hilbert transforms. The method is tested for the calculation of one-electron spectra and total energies on systems for which (essentially) exact solutions are known: the Hulth\'en potential, a free H atom, a H atom in jellium, and a Li atom in jellium. The accuracy is better and the computational speed significantly higher than that obtained with the standard Korringa-Kohn-Rostoker Green-function technique.

Self-consistent impurity calculations in the atomic-spheres approximation

The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB$_2$ is compared to first-principles calculations with the Coulomb repulsion, $\mu^\ast$, as the only parameter which is fixed to give the measured $T_c$. We solve the Eliashberg equations for both an isotropic one-band and a two-band model with different superconducting gaps on the $\pi$ and $\sigma$ Fermi surfaces. The agreement with experiments is considerably better for the two-band model than for the one-band model.

Specific heat of MgB$_2$ in a one- and a two-band model from first-principles calculations

Using the linear muffin-tin-orbital method described in the previous paper, (Phys. Rev. B 12: 3060) the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os were calculated . It is shown how the band structures of these metals may be synthesized from the sp and d bands, and the effects of hybridization, relativistic band shifts and spin--orbit coupling are illustrated by the example of Os. By making use of parameters derived from the muffin-tin potential, trends in the positions and widths of the energy bands, especially the d bands, are discussed as a function of the location in the periodic table. The densities of states of the four metals are presented and the calculated heat capacities compared with experiment. The Fermi surfaces of both Ru and Os are found to be in excellent quantitative agreement with de Haas--van Alphen measurements, indicating that the calculated d-band position is misplaced by less than 10 mRy. Very small pieces of Fermi surface, which have not yet been observed experimentally, are predicted for Os. The limited amount of experimental information available for Zr can be fairly satisfactorily interpreted if the calculated d bands, are raised by about 10--20 mRy relative tomore » the sp bands. This gives rise to a Fermi surface which is topologically equivalent to that recently found in Ti, and which does not support open orbits when the magmetic field is sufficiently great that breakdown is complete. It is suggested that the Fermi surface of Hf is probably similar, although very little experimental evidence is available for this metal. Some comments are made about the calculational method, which has proved to be physically transparent, accurate and extremely fast, and the adequancy of the standard potential, which has now been successfully employed in calculations on the great majority of the transition metals. (auth)« less

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Electronic structure of hcp transition metals

We review a simple one-electron theory of the magnetic and cohesive properties of ferro- and nearly ferromagnetic transition metals at 0 K. The theory is based on the density functional formalism, it makes use of the local spin density and atomic sphere approximations and it may, with further approximations, be reduced to the Stoner model. Results for the volume dependence of the ferromagnetic moment and the electronic pressure of bcc, fcc and hcp Fe are presented, together with theoretical values for the equilibrium atomic volume, the bulk modulus, the ferromagnetic moment, the spin susceptibility and the pressure derivatives of these quantities in Ni, Rh, Pd, Ir and Pt.

Ove Jepsen

Papers

X-ray absorption spectra: K-edges of 3d transition metals, L-edges of 3d and 4d metals, and M-edges of palladium

Self-consistent impurity calculations in the atomic-spheres approximation

Specific heat of MgB$_2$ in a one- and a two-band model from first-principles calculations

Electronic structure of hcp transition metals

Magnetic ground state properties of transition metals