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Accurate thermodynamic stability predictions enable data-driven computational materials design. Standard density functional theory (DFT) approximations have limited accuracy with average errors of a few hundred meV/atom for ionic materials, such as oxides and nitrides. Thus, insightful correction schemes as given by the coordination corrected enthalpies (CCE) method, based on an intuitive parametrization of DFT errors with respect to coordination numbers and cation oxidation states, present a simple, yet accurate solution to enable materials stability assessments. Here, we illustrate the computational capabilities of our AFLOW-CCE software by utilizing our previous results for oxides and introducing new results for nitrides. The implementation reduces the deviations between theory and experiment to the order of the room temperature thermal energy scale, i.e., ∼25 meV/atom. The automated corrections for both materials classes are freely available within the AFLOW ecosystem via the AFLOW-CCE module, requiring only structural inputs. [ABSTRACT FROM AUTHOR]

The exfoliation energy—quantifying the energy required to extract a two‐dimensional (2D) sheet from the surface of a bulk material—is a key parameter determining the synthesizability of 2D compounds. Here, using ab initio calculations, a new group of non‐van der Waals 2D materials derived from non‐layered crystals that exhibit ultra low exfoliation energies is presented. In particular for sulfides, surface relaxations are essential to correctly describe the associated energy gain needed to obtain reliable results. Taking into account long‐range dispersive interactions has only a minor effect on the energetics and ultimately proves that the exfoliation energies are close to the ones of traditional van der Waals bound 2D compounds. The candidates with the lowest energies, 2D SbTlO3 and MnNaCl3, exhibit appealing electronic, potential topological, and magnetic features as evident from the calculated band structures making these systems an attractive platform for fundamental and applied nanoscience. [ABSTRACT FROM AUTHOR]

Our first-principles study demonstrates for the first time that by increasing the molecule-surface binding strength, the interlayer magnetic coupling of a ferromagnetic metal can be drastically reduced with respect to that of a clean substrate. Importantly, for a weakly chemisorbed molecule the rehybridization of metal atomic d states within the molecule-induced surface geometry (geometrical effect) plays a crucial role in obtaining interlayer magnetic softening. On the contrary, for a strongly chemisorbed molecule the interlayer magnetic coupling is further reduced due to an interplay between the geometrical effect and the hybridization of atomic d states with molecular ones. [ABSTRACT FROM AUTHOR]

We theoretically explore through systematic multiscale ab initio and Monte Carlo calculations how the surface magnetism of a ferromagnetic surface can be fine-tuned by nonmagnetic organic molecules containing a single π bond. We demonstrate that a magnetic hardening or softening can be induced depending on the electronegativity of the heteroatom or when the π-bond "bridges" the magnetic surface atoms. Finally, the Monte Carlo simulations revealed taylored macroscopic hysteresis loops corresponding to soft and hard molecule-surface magnets. [ABSTRACT FROM AUTHOR]

The rational design of materials for organic electronics and spintronics has been a long-standing challenge. Here, we show by theoretical means how to achieve Fermi level engineering in an organic semiconductor like for instance a metal phthalocyanine. It turns out that substitution of the peripheral hydrogen atoms by either fluorine atoms or methoxy groups allows to tune the Fermi level by about 1.5 eV. Finally, we show how such tuning could be exploited to achieve a systematic way to manufacture charge and spin transfer materials by studying the system (MeO)8CoPc/F16CoPc. [ABSTRACT FROM AUTHOR]

In this paper, we present a systematic theoretical investigation of the phthalocyanine based dimer MnPcδ+/F16CoPcδ- within density functional theory framework. For all considered stacking geometries, a charge transfer from MnPc to F16CoPc is observed which is therefore identified as an intrinsic property of the molecular pair. In addition, a ferromagnetic coupling of the molecular magnetic moments within the dimer is always observed due to 90∘ superexchange and direct-exchange contributions. The comparison of the calculated absorption spectra of the different stacking arrangements to the experimentally recorded electron energy-loss spectrum strongly indicates the β stacking to be preferred over all others. Only for this geometry an experimentally observed excitation around 0.6 eV is reproduced by the calculation. [ABSTRACT FROM AUTHOR]

We have prepared mixed phthalocyanine films out of MnPc and F16CoPc, which were characterized by means of photoemission spectroscopy and electron energy-loss spectroscopy. Our data reveal the formation of MnPc/F16CoPc charge transfer dimers in analogy to the related heterojunction. The electronic excitation spectrum of these blends is characterized by a new low energy excitation at 0.6 eV. Density functional theory calculations show that the new signal is caused by a strong absorption between the states of the interface induced two level system. [ABSTRACT FROM AUTHOR]

In this ab initio study we demonstrate that molecular adsorption on a surface Rashba system can be used to modulate the surface electronic structure in different momentum space directions, i.e., to create anisotropic spin splittings in k space. This effect is rooted in the asymmetric adsorption of the molecules on the surface in a hollow site which breaks the surface symmetry. More specifically, we demonstrate that the physisorbed NH3 has a small influence on the surface Rashba states and only gives rise to variations of the surface state Rashba parameters up to a factor of 1.4 over the surface Brillouin zone. In contrast, the chemisorption of BH3 leads to variations of the Rashba parameter by more than a factor of 2.5. Consequently, the anisotropy of the Rashba-split-surface states induced by molecular adsorption also gives rise to a modulation of the surface state spin texture, i.e., the out-of-plane spin polarization varies along different k directions by up to 70% for the occupied states. This offers the possibility to change the spin direction from in-plane to predominantly out-of-plane by modifying the electronic momentum by 90°. [ABSTRACT FROM AUTHOR]

We have studied by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) single molecular spin hybrids formed upon chemisorbing a polycyclic aromatic, threefold symmetric hydrocarbon molecule on Co(111) nanoislands. The spin-dependent hybridization between the Co d states and the π orbitals of the molecule leads to a spin-imbalanced electronic structure of the chemisorbed organic molecule. Spin-sensitive measurements reveal that the spin polarization shows intramolecular variations among the different aromatic rings in spite of the highly symmetric adsorption geometry promoted by symmetry matching of the threefold symmetric molecule and the sixfold symmetric Co(111) lattice. Hence the varying degree of spin polarization on the organic molecule does not stem from a different hybridization of the aromatic rings with the Co atoms, but is proposed to be a consequence of the superposition of the spin polarization of the molecule and the spatially modulated spin polarization of the spin-dependent quantum interference pattern of the Co(111) surface state. [ABSTRACT FROM AUTHOR]

In this theoretical investigation we demonstrate that the adsorption of spatially extended two-dimensional (2D) π systems such as graphene and hexagonal boron nitride on the ferromagnetic fcc Co(111) surface leads to a specific behavior of the in-plane and interlayer Co-Co magnetic exchange interactions. More specifically, for both systems the magnetic exchange coupling within the first Co layer is enhanced, while the one between the first and the second Co layer is not modified, in contrast to the magnetic interlayer softening induced by organic molecules. Importantly, the in-plane magnetic hardening effect is mainly due to the hybridization between the pz states of the 2D π system and the d states of the Co surface. [ABSTRACT FROM AUTHOR]

Using photoelectron spectroscopy we demonstrate charge transfer at an interface between two well-known transition metal phthalocyanines, MnPc and F16CoPc, resulting in charged MnPcδ+ and F16CoPcδ- species. Moreover, the transferred charge is substantially confined to the two transition metal centers. Density functional theory calculations reveal that a hybrid state is formed between the two types of phthalocyanines, which causes this charge transfer. For the hybrid state the Mn 3dxz interacts with the Co 3dz2 orbital leading to a two-level system. As only the lower of the two hybrid states is occupied, the charge is directly transferred to the Co 3dz2 orbital. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials are frequently associated with the sheets forming bulk layered compounds bonded by van der Waals (vdW) forces. The anisotropy and weak interaction between the sheets have also been the main criteria in the computational search for new 2D systems, predicting ∼2000 exfoliable compounds. However, some representatives of a new type of non-vdW 2D systems, without layered 3D analogues, were recently manufactured. For this novel materials class, data-driven design principles are still missing. Here, we outline a set of 8 binary and 20 ternary candidates by filtering the AFLOW-ICSD database according to structural prototypes. The oxidation state of the surface cations regulates the exfoliation energy with low oxidation numbers leading to weak bonding─a useful descriptor to obtain novel 2D materials also providing clear guidelines for experiments. A vast range of appealing electronic, optical, and magnetic properties make the candidates attractive for various applications and particularly spintronics.

Using photoelectron spectroscopy we demonstrate charge transfer at an interface between two well-known transition metal phthalocyanines, MnPc and F16CoPc, resulting in charged MnPc(δ+) and F16CoPc(δ-) species. Moreover, the transferred charge is substantially confined to the two transition metal centers. Density functional theory calculations reveal that a hybrid state is formed between the two types of phthalocyanines, which causes this charge transfer. For the hybrid state the Mn 3d(xz) interacts with the Co 3d(z2) orbital leading to a two-level system. As only the lower of the two hybrid states is occupied, the charge is directly transferred to the Co 3d(z2) orbital.