Computer simulation study of the structure of the liquid-vapor interface of mercury at 20, 100, and 200 degrees C

We report the results of self-consistent quantum Monte Carlo simulations of the liquid-vapor interface of Hg. Our calculations are intended to answer two questions: (i) What is the quality of agreement between experimental da ta and calculations of the structure of the liquid-vapor interface of Hg ba sed on the best available treatment of an inhomogeneous liquid metal? (ii) How well does a theory of the liquid-vapor interface of a metal that uses a simple model local pseudopotential reproduce the predictions obtained from a theory that uses an accurate nonlocal pseudopotential? As for the liquid -vapor interfaces of other metals, we find that the density distribution al ong the normal to the liquid-vapor interface of Hg (the longitudinal densit y distribution) is stratified, with a penetration depth into the bulk liqui d of about three layers. The use of a nonlocal pseudopotential in the self- consistent Monte Carlo simulations leads to very good agreement between the calculated and observed longitudinal density distributions. We also show t hat the use of a model local pseudopotential leads to a qualitatively corre ct description of the longitudinal density in the liquid-vapor interface of Hg. When the model local pseudopotential is used, the locations of the str ata in the longitudinal density distribution are correct but the peak heigh ts are too large and the peak widths are too small. The largest part of the error arising from the use of the model local pseudopotential can be trace d to the error in the predicted surface tension. The quality of the agreeme nt between simulations based on the best nonlocal pseudopotential and those based on a simple model local pseudopotential is sufficient to make the la tter a very useful tool for inferring the qualitative properties of a broad class of inhomogeneous liquid metals and alloys. We also report the result s of calculations of the transverse (in-plane) structure of the liquid-vapo r interface of Hg, for several slices of the interface. Except in the outer most layer, the transverse pair correlation function is found to be indisti nguishable for the bulk liquid pair correlation function, in agreement with the available experimental data. Unlike the case of the liquid-vapor inter face of alkali metals, our results imply there is a nontrivial difference b etween the transverse pair correlation function in the outermost layer of t he liquid-vapor interface of Hg and that in the bulk liquid. The difference takes the form of an exaggerated shoulder on the first peak of the pair co rrelation function and is of the type which some investigators believe is a ssociated with dimerization. However, we can fmd no direct evidence for dim er formation in images from our simulations of the positions of the ion cor es in the outermost layer of the liquid-vapor interface of Hg. [S1063-651X( 99)04401-3].