Nature of the surface-reconstruction phase transition and the high-temperature phase of clean W(001)

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Abstract
A short-range model for the W(001) reconstruction phase transition is presented and its properties are analyzed by means of a Monte Carlo calculation. The latter determines ordering properties as well as properties that reveal the local character of the atomic displacements, including the integer-order diffraction beams and distributions of displacements. New measurements of the behavior of the integer beams through the transition are also presented and interpreted in terms of the simulation results. The question of the character of the transition, displacive or order-disorder, is discussed from the perspective in which those two possibilities are limiting cases. Variation along this spectrum is determined by important physical characteristics of the electronic driving force. Implications of our results for the proper understanding of the Debye-Waller behavior of W(001) and for measurements of critical exponents in this system are also discussed.