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.

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

In this work we reexamine the LDA+U method of Anisimov and coworkers in the framework of a plane-wave pseudopotential approach. A simplified rotational-invariant formulation is adopted. The calculation of the Hubbard U entering the expression of the functional is discussed and a linear response approach is proposed that is internally consistent with the chosen definition for the occupation matrix of the relevant localized orbitals. In this way we obtain a scheme whose functionality should not depend strongly on the particular implementation of the model in ab-initio calculations. We demonstrate the accuracy of the method, computing structural and electronic properties of a few systems including transition and rare-earth correlated metals, transition metal monoxides and iron-silicate.

First-principles calculations within the Local Density Approximation (LDA) or Generalized Gradient Approximation (GGA), though very successful, are known to underestimate redox potentials, such as those at which lithium intercalates in transition metal compounds. We argue that this inaccuracy is related to the lack of cancellation of electron self-interaction errors in LDA/GGA and can be improved by using the DFT+U method with a self-consistent evaluation of the U parameter.We show that, using this approach, the experimental lithium intercalation voltages of a number of transition metal compounds, including the olivine Li x MPO 4 (M=Mn, Fe Co, Ni), layered Li x MO 2 (x =Co, Ni) and spinel-like Li x M 2 O 4 (M=Mn, Co), can be reproduced accurately.

The aim of this review article is to assess the descriptive capabilities of the Hubbard-rooted LDA1U method and to clarify the conditions under which it can be expected to be most predictive. The article illustrates the theoretical foundation of LDA1U and prototypical applications to the study of correlated materials, discusses the most relevant approximations used in its formulation, and makes a comparison with other approaches also developed for similar purposes. Open "issues" of the method are also discussed, including the calculation of the electronic couplings (the Hubbard U), the precise expression of the corrective functional and the possibility to use LDA1U for other classes of materials. The second part of the article presents recent extensions to the method and illustrates the significant improvements they have obtained in the description of several classes of different systems. The conclusive section finally discusses possible future developments of LDA1U to further enlarge its predictive power and its range of applicability.

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.

Transition-metal centers are the active sites for many biological and inorganic chemical reactions. Notwithstanding this central importance, density-functional theory calculations based on generalized-gradient approximations often fail to describe energetics, multiplet structures, reaction barriers, and geometries around the active sites. We suggest here an alternative approach, derived from the Hubbard U correction to solid-state problems, that provides an excellent agreement with correlated-electron quantum chemistry calculations in test cases that range from the ground state of Fe2 and Fe − 2 to the addition-elimination of molecular hydrogen on FeO + . The Hubbard U is determined with a novel self-consistent procedure based on a linear-response approach.Transition metals are central to our understanding of many fundamental reactions, as active sites in naturallyexisting or synthetic molecules that range from metalloporphyrins and oxidoreductases [1] In this Letter, we argue that generalized gradient approximations (GGA) [8] augmented by a Hubbard U term [9], already very successful in the solid state [10,11], also greatly improve single-site or few-site energies, thanks to a more accurate description of self-and intraatomic interactions. Nevertheless, U is not a fitting parameter, but an intrinsic response property: as shown by Cococcioni and de Gironcoli [12], U measures the spurious curvature of the GGA energy functional as a function of occupations, and GGA+U largely recovers the piecewise-linear behavior of the exact ground-state energy. U is determined by the difference between the screened and bare second derivative of the energy with respect to on-site occupations λ I T = i λ I i (i is the spinorbital, and I the atomic site) [12]. While in the original derivation U was calculated from the GGA ground state, we argue here that U should be consistently obtained from the GGA+U ground state itself. This becomes especially relevant when GGA and GGA+U differ qualitatively (metal vs. insulator in the solid state, different symmetry in a molecule). To clarify our approach, we first identify in the GGA+U functional the electronic terms that have quadratic dependence on the occupations:

We report on a significant failure of the local density approximation (LDA) and the generalized gradient approximation (GGA) to reproduce the phase stability and thermodynamics of mixed-