For the first time first-principles calculations were performed to get the dependences of strain energy and band gap of achiral nanotubes obtained by rolling up monolayers of gallium (II) sulfide and selenide. The hybrid density functional method (with 13% of the Hartree-Fock exchange) within the CRYSTAL17 computer code was used. The empirical Grimme correction was applied to describe the dispersion interactions between layers accurately. As a result of simulations of nanotubes with different chirality and different diameters, the minimum diameters of the stable single-walled nanotubes were determined, which retain the continuity of the chemical bonds on the outer nanotube surface. It was shown that the strain energy dependence on a diameter obeys a classical law of inverse squares and is the same for «zigzag» and «armchair» nanotubes.
A force field is proposed that reproduces with a high accuracy a large number of properties of the bulk crystal MoS_2 phases, monolayers, and nanotubes. The reproduced values are both the experimental results and the results of quantum chemical calculations. The elaborated interaction potential can be useful primarily for investigation of multiwall MoS_2 nanotubes and their thermodynamic properties, especially, since the potential is able to reproduce the frequencies of the crystal phonon spectrum. In this study the proposed potential is applied to simulate the temperature dependence of a number of properties of the armchair and zigzag nanotubes. The calculations have been performed using molecular mechanics method within the framework of quasi harmonic approximation which is carried out through the estimation of the temperature dependence of the Helmholtz free energy.
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