Site occupancy pair correlation functions and structure factors of partially ordered overlayers: II. Application to O/Ni(100)

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Abstract This paper is the second part of a work devoted to the computation of the diffuse LEED intensities obtained from partially ordered overlayers deposited at single crystal surfaces. We are particularly interested in the cases where this computation requires the knowledge of the statistical distribution of occupied chemisorption sites. In the first part of this work, we have provided an accurate theoretical description of two approximate methods for determining the structure factors and the related site occupancy pair correlation functions: a method based upon a self-consisted molecular field approximation and a cumulant expansion method. In the second part, we specify the validity domain of these methods in the simple case where one species is chemisorbed at one type of site. This is achieved by comparing their results with those obtained from a Monte Carlo simulation, the latter being regarded as reference results. When the order range in the overlayer is about the interatomic distance, both approximate methods lead to results very close to those obtained from a Monte Carlo simulation. However, discrepancy progressively increases when the arrangement of the adlayer approaches a superstructure. So, when the order range is greater than a few interatomic distances, they are no longer usable and the diffuse LEED intensity calculation has to resort to a Monte Carlo simulation. We give an illustration of the influence or the local order in the particular case O/N(100).