What is the best way to find the global minimum structure(or get close to it) for an ion and N waters? (i.e. ion cluster in vacuum)

  • For example, consider Flouride ion cluster with N=5 waters.
  • I want to determine the global minimum structure (using Gaussian09 for a given level of theory and basis set).
  • This helped me get started (Geometry optimization: dependence on initial geometry), but initial geometry sampling is easier for molecules compared to clusters.
    • What is an intelligent way to generate reasonable initial configurations for this cluster (say for N=4,5,6)?
    • Constraint: My computational resources allows me to optimize about 10 structures at a given time for a reasonable level of DFT theory. I might be able to do a maximum of 100-200 optimizations.
  • $\begingroup$ @AjayMurlidharan Welcome to the site! If haven't yet, visit the help center and take the tour. Not my area of expertise, but my understanding is people usually obtain reasonable starting geometries by running Molecular dynamics simulations. $\endgroup$ – Tyberius Jun 22 '18 at 18:10
  • $\begingroup$ @Tyberius: Thanks! Also, I thought about this. I already have an ab-initio MD trajectory (~50 ps) of the ion in bulk water (Flouride ion and 64 waters with Periodic boundary conditions). I could in principle sample cluster configurations from here. Trying to figure out if this is the best way with my computational resource limitations. $\endgroup$ – Ajay Muralidharan Jun 22 '18 at 18:30
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    $\begingroup$ Finding a global minimum of (generalizing here) a many-dimensional function is a great problem in numerical methods. In my opinion, a good place to start reading is about simulated annealing, which is commonly used in optimizing molecular configurations. $\endgroup$ – pentavalentcarbon Jun 23 '18 at 1:57

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