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An analytic modified embedded atom method (MEAM), developed for bulk alkali metals, is used to identify up to six different, energetically lowest isomers of Li N and Na N clusters (N = 2 − 150) within an unbiased global structure-optimization procedure. Randomly generated clusters are locally optimized using the quasi-Newton method and the resulting six most stable isomers are used afterwards in the Aufbau–Abbau algorithm. Due to its analytical formulae and its semiempirical nature, the MEAM emerges as a fast and efficient method that is particularly suitable for an unbiased global optimization. Structural and energetic analyses show that the MEAM provides compact clusters that are in good agreement with the results of other semiempirical calculations. Occasionally, the MEAM produces structures that are normally not found with such model potentials but in more accurate DFT or ab initio studies. Moreover, clusters of pronounced stability (magic sizes) are identified, growth patterns are studied, and trends can be recognized in which the atomic arrangement within the clusters of the considered size range corresponds more to the fcc than to the bcc packing. Additionally, for most cluster sizes the structures of the lowest-energy isomers of Li N and Na N clusters are very similar.

Several lines of evidence suggest that brain serotonergic systems may be disturbed in obsessive compulsive disorder (OCD). The serotonergic system strongly affects sleep and characteristic abnormalities of sleep are documented in depression. This study, therefore, aimed to investigate sleep structure of OCD patients in order to evaluate whether similar changes as in depression are present. Up to now, this issue has been addressed only in few studies with small numbers of patients. Sleep patterns of 62 unmedicated patients with primary OCD and 62 age- and sex-matched healthy controls were investigated by polysomnography. Additionally, the impact of tryptophan depletion on sleep was studied in a subgroup of 12 OCD patients and 12 controls. The OCD patients exhibited moderate, but significant disturbances of sleep continuity measures but no abnormalities of slow wave sleep or REM sleep, except a significant elevation of 1st REM density. Tryptophan depletion induced a worsening of sleep continuity, but no changes of REM sleep or slow wave sleep. Assuming that changes of sleep architecture indicate underlying neurobiological abnormalities, this study indicates that neurobiological disturbances are different in primary OCD as compared with primary depression.