Magnetic structure of a multiferroic compound: CuOCl.

The CuOCl compound has been shown to be a high-temperature spin-driven multiferroic system, with a linear magneto-electric coupling. In this paper we propose a complete study of its magnetic structure. We derive the low energy magnetic Hamiltonian using multi-reference configuration interaction and the spin structure using Monte-Carlo simulations.

Why the pyrochlore-like antiferromagnet NaCuFis magnetically non-frustrated.

We present a theoretical study of the magnetic properties for the pyrochlore-like NaCuFcompound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated usingmethods explicitly treating the electronic correlation. A model Hamiltonian (quantum Heisenberg Hamiltonian, and for comparison a spin 1/2 Ising Hamiltonian) was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field.

The OpenMolcas : A Community-Driven Approach to Advancing Computational Chemistry.

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.

For an ab initio calculation of the magnetic excitations: RelaxSE!

In this paper, we present a novel efficient and parallel implementation, RelaxSE, for the calculation of the low-lying excited states and energies of strongly correlated systems. RelaxSE is based on the fully uncontracted multi-reference method of Selected Active Space + Single excitations. This method has been specifically designed to be able to tackle systems with numerous open shells per atoms.

Pressure-dependent X-ray diffraction of the multiferroics RMnO.

The room-temperature structural properties of the RMnO multiferroics have been investigated under pressure, using powder X-ray scattering and density functional theory (DFT) calculations. It was possible to determine the lattice parameters and the main atomic positions as a function of pressure. Good agreement was observed between the X-ray and DFT results for most of the determined crystallographic data.

Orbital-ordering-driven multiferroicity and magnetoelectric coupling in GeV₄S₈.

We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I orbital order system GeV₄S₈. Our study demonstrates that this clustered compound displays a para-ferroelectric transition at 32 K. This transition originates from an orbital ordering which reorganizes the charge within the transition metal clusters.

Analysis of the multiferroicity in the hexagonal manganite YMnO3.

We performed magnetic and ferroelectric measurements, associated with Landau theory and symmetry analysis, in order to clarify the situation of the YMnO3 system, a classical example of type I multiferroics. We found that the only magnetic group compatible with all experimental data (neutron scattering, magnetization, polarization, dielectric constant, second harmonic generation) is the P6'(3) group. In this group a small ferromagnetic component along c is induced by the Dzyaloshinskii-Moriya interaction, and observed here in magnetization measurements.

Interface effects in perovskite thin films.

The control of matter properties (transport, magnetic, dielectric,…) using synthesis as thin films is strongly hindered by the lack of reliable theories, able to guide the design of new systems, through the understanding of the interface effects and of the way the substrate constraints are imposed on the material. The present Letter analyzes the energetic contributions at the interfaces, and proposes a model describing the microscopic mechanisms governing the interactions at an epitaxial interface between a manganite and another transition metal oxide in perovskite structure (as for instance SrTiO3). The model is checked against experimental results and literature analysis.

The dehydration of SrTeO3(H2O)--a topotactic reaction for preparation of the new metastable strontium oxotellurate(IV) phase ε-SrTeO3.

Microcrystalline single-phase strontium oxotellurate(IV) monohydrate, SrTeO(3)(H(2)O), was obtained by microwave-assisted hydrothermal synthesis under alkaline conditions at 180 °C for 30 min. A temperature of 220 °C and longer reaction times led to single crystal growth of this material. The crystal structure of SrTeO(3)(H(2)O) was determined from single crystal X-ray diffraction data: P2(1)/c, Z = 4, a = 7.

An ab initio evaluation of the local effective interactions in the NaxCoO2 family.

We used quantum chemical ab initio methods to determine the effective parameters of Hubbard and t-J models for the Na(x)CoO(2) compounds (x = 0 and 0.5). As for the superconducting compound we found the a(1g) cobalt orbitals above the e'(g) ones by a few hundreds of meV due to the e'(g)-e(g) hybridization of the cobalt 3d orbitals.

Large increase of the curie temperature by orbital ordering control.

Using first principle calculations we showed that the Curie temperature of manganites thin films can be increased by far more than an order of magnitude by applying appropriate strains. Our main breakthrough is that the control of the orbital ordering responsible for the spectacular T{C} increase cannot be imposed by the substrate only. Indeed, the strains, first applied by the substrate, need to be maintained over the growth direction by the alternation of the manganite layers with another appropriate material.

Fast calculation of the electrostatic potential in ionic crystals by direct summation method.

An efficient real space method is derived for the evaluation of the Madelung's potential of ionic crystals. The proposed method is an extension of Evjen's method. It takes advantage of a general analysis of the potential convergence in real space.

Influence of the incommensurability in Sr14-xCaxCu24O41 Family Compounds.

We study the influence of the structural modulation on the low energy physics of the Sr14-xCaxCu24O41 oxides, using ab initio determination of the on-site and nearest-neighbor effective parameters. The structural modulations appear to be the key degree of freedom responsible for the low energy properties, such as the electron localization, the formation of dimers in the x=0 compound, or the antiferromagnetic order in the x=13.6 compound.

Ab initio evaluation of the charge ordering in alpha'NaV2O5.

We report ab initio calculations of the charge ordering in alpha'NaV2O5 using large configurations interaction methods on embedded fragments. Our major result is that the 2p(y) electrons of the bridging oxygen of the rungs present a very strong magnetic character and should thus be explicitly considered in any relevant effective model. The most striking consequence of this result is that the spin and charge ordering differ substantially, as differ the experimental results depending on whether they are sensitive to the spin or charge density.