RESUMEN
A simple lattice model of metal-organic adsorption layers self-assembling on a Au(111) surface and based on pyridyl-substituted porphyrins differing in the number of functional groups and their position has been proposed. The model has been parameterized using DFT methods. The ground state analysis of the considered model demonstrates the variety of surface-confined metal-organic networks (SMONs) containing square, linear, and discrete elements appearing in the adsorption layer depending on the partial pressure of the components. The SMONs comprising more symmetrical molecules with a greater number of pyridyl substituents in the porphyrin core exhibit more diverse phase behavior. Structures of the phase diagrams were verified at nonzero temperatures using Grand Canonical Monte Carlo simulations. It was found that the continuous SMONs have higher thermal stability at relatively low partial pressures of the organic component, while the linear and discrete SMONs are more thermally stable at high pressure. Depending on the partial pressure of the organic component, thermal destruction of continuous SMONs occur either through the formation of defects/islands having structures of the linear SMONs, or through the sublimation of individual structural elements. Melting of linear SMONs reveals the appearance of 2D pores or islands of a purely organic phase. The latter fact is confirmed by the experimentally observed coexistence of these phases.
RESUMEN
We present to the scientific community the Surface Science Modeling and Simulation Toolkit (SuSMoST), which includes a number of utilities and implementations of statistical physics algorithms and models. With SuSMoST it is possible to predict or explain the structure and thermodynamic properties of adsorption layers. SuSMoST automatically builds formal graph and tensor-network models based on atomic description of adsorption complexes and helps to do ab initio calculations of interactions between adsorbed species. Using methods of various nature SuSMoST generates representative samples of adsorption layers and computes its thermodynamic quantities such as mean energy, coverage, density, and heat capacity. From these data one can plot phase diagrams of adsorption systems, assess thermal stability of self-assembled structures, simulate thermal desorption spectra, and so forth.
RESUMEN
In this study, we identified stable configurations for three nanoparticle structure motifs (icosahedral, decahedral and cuboctahedral) of eight transition metals (Cu, Ag, Au, Pd, Ni, Rh, Ir, and Pt) ranging in size from 140 to 3000 atoms. We made simple yet precise analytical approximations of the energy of the stable configurations as a function of nanoparticle size and calculated the structure crossover sizes from these approximations. We then analyzed the surface structure of the nanoparticles in terms of the distribution of the coordination numbers and active sites. We found that low-coordinated atoms are most preferable for cuboctahedral forms and for lighter metals - Cu, Ni and Rh. Compared to other considered metals, gold nanoparticles exhibited unique features as follows: the least amount of low-coordinated atoms, the largest fraction of (111) faces on its surface and a concave reconstruction of five-fold vertices.