Abstract
We report results of an orbital-free ab initio molecular dynamics (OF-AIMD) study of the free liquid surface (FLS) of Sn at 1000 K and 600 K. A key ingredient in the OF-AIMD method is the local pseudopotential describing the ions-valence electrons interaction. We have used a force-matching method to derive a local pseudopotential suitable to account for the variation of the forces from the bulk to the FLS. We obtain very good results for structural properties, such as the reflectivity, including the characteristic shoulder it presents in x-ray experiments. Moreover we have been able to study ab initio for the first time the evolution in some dynamical properties as we move from the central region, where the system behaves like the bulk liquid, to the FLS.
Highlights
Molecular dynamics (MD) simulations have become an essential technique in the study of a wide variety of condensed matter systems, and during the last three decades there has been an increasing amount of systems studied by using ab initio molecular dynamics (AIMD) methods based on density functional theory (DFT) [1]
Most AIMD methods are based on the Kohn-Sham (KS) orbital representation of DFT (KS-AIMD methods) which, very accurate, imposes high computational demands that severely limit the size of the systems to be studied as well as the extent of the simulation times
This improvement is achieved at the price of resorting to an approximate description of the electronic kinetic energy, and in principle, the orbital-free ab-initio molecular dynamics (OF-AIMD) approach is less accurate than the KS-AIMD method
Summary
Molecular dynamics (MD) simulations have become an essential technique in the study of a wide variety of condensed matter systems, and during the last three decades there has been an increasing amount of systems studied by using ab initio molecular dynamics (AIMD) methods based on density functional theory (DFT) [1]. The OF-AIMD method substantially reduces the number of variables needed to describe the electronic state and allows to study larger systems for longer simulation times This improvement is achieved at the price of resorting to an approximate description of the electronic kinetic energy, and in principle, the OF-AIMD approach is less accurate than the KS-AIMD method. Despite this caveat, the OF-AIMD has provided good descriptions for several static and dynamic properties of a variety of bulk simple liquid metals [3, 4] and free liquid surfaces (FLS) [5]. After the force matching process, these forces are recovered and the ones in the bulk are improved
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