Intense experimental and theoretical studies have demonstrated that the anisotropic triangular lattice as realized in the κ-(BEDT-TTF)2X family of organic charge transfer (CT) salts yields a complex phase diagram with magnetic, superconducting, Mott insulating and even spin liquid phases. With extensive density functional theory (DFT) calculations we refresh the link between manybody theory and experiment by determining hopping parameters of the underlying Hubbard model. This leads us to revise the widely used semiempirical parameters in the direction of less frustrated, more anisotropic triangular lattices. The implications of these results on the systems' description are discussed.PACS numbers: 74.70. Kn,71.10.Fd,71.15.Mb,71.20.Rv A strong research trend of the new millennium has been the desire to understand complex manybody phenomena like superconductivity and magnetism by realistic modelling, i.e. to employ precise first principles calculations to feed the intricate details of real materials into the parameter sets of model Hamiltonians that are then solved with increasingly powerful manybody techniques. The κ-(BEDT-TTF) 2 X [1] organic charge transfer salts are a perfect example for a class of materials with such fascinating properties that they drive progress in experimental and manybody methods alike. Experimentally, the phase diagram shows Mott insulating, superconducting, magnetic and spin liquid phases [2,3,4,5]. Theoretically, the underlying anisotropic triangular lattice is a great challenge due to effects of frustration and the intense efforts to get a grip on the problem include studies with path integral renormalization group (PIRG) [6], exact diagonalization [7], variational Monte Carlo [8], cluster dynamical mean field theory [9, 10] and dual Fermions [11] to cite a few. In this rapidly expanding field of research, electronic structure calculations play the decisive role of mediating between the complex underlying structure and phenomenology of organic charge transfer salts and the models used for understanding the physics [12], and in this work, we will provide the perspective of precise, state of the art electronic structure calculations.Previously, κ-type CT salts have been investigated by semi-empiricial and first principles electronic structure calculations. The most commonly used t, t ′ , U parameter sets derive from extended Hückel molecular orbitals calculations [13,14] performed on different constellations of BEDT-TTF dimers.The main result reported here is that our first principles study shows all four considered κ-type CT salts to be less frustrated than previously assumed based on semiempirical theory. Most importantly, the often cited value of t ′ /t = 1.06 [13] for the spin liquid material κ-(ET) 2 Cu 2 (CN) 3 should be replaced by the significantly smaller value t ′ /t = 0.83 ± 0.08. This has fundamental implications on the systems' model description as we shall see below.In this Letter, we employ the Car-Parrinello [15] projector-augmented wave [16] molecular dynamics (CPMD)...

The natural mineral azurite Cu(3)(CO(3))(2)(OH)(2) is a frustrated magnet displaying unusual and controversially discussed magnetic behavior. Motivated by the lack of a unified description for this system, we perform a theoretical study based on density functional theory as well as state-of-the-art numerical many-body calculations. We propose an effective generalized spin-1/2 diamond chain model which provides a consistent description of experiments: low-temperature magnetization, inelastic neutron scattering, nuclear magnetic resonance measurements, magnetic susceptibility as well as new specific heat measurements. With this study we demonstrate that the balanced combination of first principles with powerful many-body methods successfully describes the behavior of this frustrated material.

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weighted by cyclical constrains. Furthermore, the approach proposed by Schumpeter embodies another fundamental idea, which is the competition between innovators. Indeed, these players pursue the monopoly rents that accrue to new proprietary technologies, and, as such, intend to be the fi rst to fi nd the right solution to the right problem at the right moment. Economists have been studying the relationship between innovation and competition for many years, trying to understand more specifi cally whether competition fosters innovation or not. As a matter of fact, some concluded on a negative infl uence of competition upon innovation and some on a positive effect. [ 2,5 ] But it appears that many economists and marketers converge toward the idea that the innovation versus competition curve shows an inverted U shape. [ 6 ] In other words some competition is constructive, yet aggressive competition tends to hamper the innovation process.It is interesting to place in this context the concept of duplication. Historians and sociologist often refer to multiple discoveries for cases in which similar discoveries are made simultaneously by scientists working independently from each other. [ 7 ] The wide literature of scientifi c discovery can be classifi ed into three basic categories: [ 8 ] the genius model, [ 9 ] the model based on chance, [ 10 ] and the model relying on cultural maturation. [ 11 ] The latter type, which is the more prone to multiplicity, suggests that the contributions of individual researcher are epiphenomenal. This school of thought advocates the infl uence of social determinism and zeitgeist. [ 12 ] As a consequence, it proposes that the change in science is strongly infl uenced by cultural priorities and research programs. [ 8 ] This very type of duplication can be considered benefi cial for society as a higher number of independent experiments does maximize the probability of the accuracy and the reality of a given discovery. [ 11 ] This point of view is easily applicable to paradigm shifting, major discoveries, especially if they occurred before the era of easily accessible information via the internet, gigantic centralized databases, and ultrafast search engines. However, nowadays it may appear obvious that the replication of the effort to generate innovation is socially suboptimal and reduces the overall return on investment for entities that fi nance research. None of the studies mentioned above accounts for that phenomenon because of the diffi culty to quantify modern duplication. Thus, despite its acknowledged relevance [ 13 ] and occurrence, the share and infl uence of modern duplication in academic and industrial research remains largely underexplored. The European Patent Offi ce (EPO) affi rms that "up to 30% of all expenditure in R&D is wasted on redeveloping existing Copper sulfi des and copper selenides have recently been reported as new and promising low-cost and environmentally friendly thermoelectric materials. Here, it is shown that these materials have actually been studied for mo...

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On the basis of electronic structure calculations we identify the superconductivity in the novel, high-temperature superconductor PuCoGa5 to be caused by the pairing of Pu 5f electrons. Assuming delocalized Pu 5f states, we compute theoretical crystallographic constants very near to the experimental ones, and the calculated specific heat coefficient compares reasonably to the measured coefficient. The theoretical Fermi surface is quasi-two-dimensional and the material appears to be close to a magnetic phase instability.

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Using ab initio molecular dynamics we investigate the electronic and lattice structure of AFe 2 As 2 ͑A =Ca,Sr,Ba͒ under pressure. We find that the structural phase transition ͑orthorhombic to tetragonal symmetry͒ is always accompanied by a magnetic phase transition in all the compounds while the nature of the transitions is different for the three systems. Our calculations explain the origin of the existence of a collapsed tetragonal phase in CaFe 2 As 2 and its absence in BaFe 2 As 2 . We argue that changes in the Fermi-surface nesting features dominate the phase transitions under pressure rather than spin frustration or a Kondo scenario. The consequences for superconductivity are discussed.The discovery of iron pnictide superconductors 1 with critical temperatures T c up to 57.4 K ͑Ref. 2͒ upon doping has strongly revived the interest in high-T c superconductivity. The undoped Fe-based parent compound undergoes at low temperatures a structural transition from tetragonal to orthorhombic symmetry accompanied by a magnetic phase transition to a stripe-type spin-density-wave state. 3-7 While the nature of these two transitions is different between LaFeAsO ͑1111 compound͒ and AFe 2 As 2 ͑122 compound͒ with A = ͑Ba, Sr, Ca͒, superconductivity appears in both material classes only when the lattice distortion and magnetic ordering are suppressed, indicating a strong competition between the structural distortion, magnetic ordering, and superconductivity in iron pnictides.Recently, superconductivity in the parent compounds 1111 and 122 was reported under application of pressure. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In LaFeAsO, 8 resistivity measurements show superconductivity at Ϸ12 GPa with T c = 21 K. In BaFe 2 As 2 superconductivity is found to appear gradually with increasing pressure while in SrFe 2 As 2 the onset of superconductivity occurs abruptly. 22 In CaFe 2 As 2 , 12-14 detailed neutron-and x-ray diffraction analysis shows that the system undergoes a first-order phase transition from a magnetic orthorhombic to a nonmagnetic "collapsed" tetragonal phase under pressure. The possible appearance of superconductivity in this collapsed tetragonal phase is presently under debate. 15,16 While various experiments give different values of critical pressures 17-25 due to the fact that the phase transition is sensitive to possible nonhydrostatic pressure effects, Sn content in some samples, or the use of single crystals or polycrystalline material for structure determination, it is claimed that BaFe 2 As 2 and SrFe 2 As 2 do not manifest a collapsed tetragonal phase at elevated pressure. 13,17,18,23,24 Therefore, the fact that structurally similar compounds exhibit phase transitions of different nature urgently calls for a theoretical understanding. Moreover, it is still under intensive debate which is the driving mechanism of the collinear stripe-type antiferromagnetic ordering; whether the Fermi-surface nesting or the competition of exchange antiferromagnetic interactions between the ...