The magnetocaloric effect, that consists of adiabatic temperature changes in a varying external magnetic field, appears not only when the amplitude is changed, but in cases of anisotropic magnetic materials also when the direction is varied. In this article we investigate the magnetocaloric effect theoretically for the archetypical single molecule magnets Fe 8 and Mn 12 that are rotated with respect to a magnetic field. We complement our calculations for equilibrium situations with investigations of the influence of non-equilibrium thermodynamic cycles.

Background: Classical carbon potentials together with classical molecular dynamics are employed to calculate structures and physical properties of such carbon-based materials where quantum mechanical methods fail either due to the excessive size, irregular structure or long-time dynamics.Examples are given by recently synthesized free-standing carbon nanomembranes (CNM) with molecular thickness and macroscopic lateral size as well as by amorphous carbon.Results: Although such potentials, as for instance implemented in LAMMPS, yield reasonably accurate bond lengths and angles for several carbon materials such as graphene, it is not clear how accurate they are in terms of mechanical properties such as Young's moduli. We performed largescale classical molecular dynamics investigations of three carbon-based materials using the various potentials implemented in LAMMPS as well as the highly sophisticated EDIP potential of Nigel Marks. We demonstrate how the Young's moduli vary with classical potentials and compare to experimental results. Conclusion:Since classical descriptions of carbon are bound to be approximations it is not astonishing that different realizations yield differing results. One should therefore carefully check for which observables a certain potential is suited. We hope to contribute to such a clarification. 1 arXiv:1707.02179v1 [cond-mat.mtrl-sci]

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Ultrathin membranes with subnanometer pores enabling molecular size-selective separation were generated on surfaces via electron-induced cross-linking of self-assembled monolayers (SAMs). The evolution of p-terphenylthiol (TPT) SAMs on Au(111) surfaces into cross-linked monolayers was observed with a scanning tunneling microscope. As the irradiation dose was increased, the cross-linked regions continued to grow and a large number of subnanometer voids appeared. Their equivalent diameter is 0.5 ± 0.2 nm and the areal density is ≈1.7 × 1017 m−2. Supported by classical molecular dynamics simulations, we propose that these voids may correspond to free volumes inside a cross-linked monolayer.