A 2D array of electronically coupled quantum boxes is fabricated by means of on-surface self-assembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes.

A rather rare phenomenon of an opening of the spin gap in transition metal oxides was observed in pyroxene NaTiSi 2 O 6 and was interpreted as a formation of singlet Ti-Ti dimers [1,2]. However, in the recent Letter [3] the authors challenged this picture. On the basis of spin polarized GGA calculations they argued that with decrease of the temperature this compound evolves into a Haldane phase, characterized by formation of onedimensional S=1 chains.This novel interpretation, however, is highly questionable. The authors claim that "direct overlap between 3d orbitals centered on closer Ti ions, ..., indicates that two electrons of the same spin, occupying those states, are shared by two Ti ions" (cursive ours). This picture however contradicts typical situation for shorts metalmetal bonds in insulating solids, especially those of spin S = 1/2 ions.Most probably the defect lies in the neglect of electronic correlations in the calculation method used in [3]. NaTiSi 2 O 6 is known to be strong Mott insulator with the energy gap close to 2 eV [4], whereas the calculations of Ref. 3 lead to very small energy gaps 0.2-0.3 eV.In order to take into account strong electronic correlations in Ti-3d shell, we performed for the LT phase (T=100 K) of NaTiSi 2 O 6 the LDA+U calculations [5], which was proven very successful in similar cases [6,7,8] The calculation scheme was realized in the framework of the linear muffin-tin orbitals method [9]. Crystal structure parameters were taken from Ref. 10. The values of on-cite Coulomb interaction U = 3.3 eV and Hund's rule exchange J H = 0.8 eV parameters for Ti-3d shell were obtained in constrained supercell calculation [7].In contrast to Ref. 3, the fully antiferromagnetic state (AFM) was found to have lowest total energy (see Tab.1). The total energy of F+AF state (ferromagnetically coupled antiferromagnetic dimers on short Ti-Ti bonds) is just a little bit larger. This indicates that the coupling between dimers is pretty small, J inter = 7 K. On the contrary, the exchange interaction within Ti dimers is antiferromagnetic and rather strong: from the comparison of total energies of totally AFM and AF+F states we find J intra = 626 K. Direct calculation of exchange integrals using the scheme of Ref. In conclusion, we stress that by neglecting correlation effects [3]

Synergistically acting weak molecular interactions create robust free-standing monolayers via self-assembly.

Determining the scattering potential landscape for two-dimensional superlattices provides key insight into fundamental quantum electron phenomena. Theoretical and semiempirical methods have been extensively used to simulate confinement effects of the two-dimensional electron gas (2DEG) on superlattices with a single scatterer in the form of vicinal surfaces and dislocation networks or isolated structures such as quantum corrals and vacancy islands. However, the complexity of the problem increases when the building blocks (or scatterers) are heterogeneous, as in metal-organic nanoporous networks (MONNs), since additional potentials may come into play. Therefore, the parametrization of the surface potential landscape is often inaccurate, leading to incorrect scattering potentials. Here, we address this issue with a combination of scanning tunneling microscopy/spectroscopy, angle resolved photoemission spectroscopy and Kelvin probe force microscopy measurements together with electron plane-wave expansion simulations on a MONN grown on Cu(111). This experimentaltheory approach, enables us to capture the 2DEG response to the intricate scattering potential landscape, and reveals systematic modeling procedures. Starting from a realistic geometry of the system, we determine the repulsive scattering potentials for both molecules and coordinated metal adatoms, the latter contradicting the established simulation framework. Moreover, we reveal local asymmetries and subtle renormalization effects of the 2DEG that relate to the interaction of the MONN and the underlying substrate.

We show that highly ordered two-dimensional (2D) chessboard arrays consisting of a periodic arrangement of two different molecules can be obtained by self-assembly of unsubstituted metal-phthalocyanines (metal-Pcs) on a suitable substrate serving as the template. Specifically, CuPc + MnPc and CuPc + CoPc mixtures sort into highly ordered Cu/Mn and Cu/Co chessboard arrays on the square p(10 × 10) reconstruction of bismuth on Cu(100). Such created bimolecular chessboard assemblies emerge from the site-specific interactions between the central transition-metal ions and the periodically reconstructed substrate. This work provides a conceptually new approach to induce 2D chessboard patterns in that no functionalization of the molecules is needed.