Boreskov

PP‐9MODELING THE CONFIGURATIONS OF WATER MOLECULESIN CLATHRATE HYDRATE CRYSTALSDzyabchenko A.V.*, Kadyshevich E.A.**, Kuznetsov K.P.***, Askhabov A.M.****L.Ya. Karpov Institute of Physical Chemistry, Moscow, Russia**A.M. Obukhov Institute of Atmospheric Physics of RAS, Moscow, Russia***Institute of Geology Komi SC UB RAS, Syktyvkar, RussiaThe various clathrate hydrates represent the class of solid supramolecular host–guestcompounds. Their crystal structures are known as polyhedral cages built of water moleculesconnected with one another by strong hydrogen bonds while the polyhedral cavities areoccupied by guest organic molecules, contacting with the host molecules by weak van derWaals forces. The methane clathrate hydrates occur in nature in huge amounts. The regionsof their occurrence on our planet are sea floor deposits and permafrost zones grounds. Inlife sciences, the interest to the clathrate hydrates is connected with a hypothesis of lifeorigin [1], which proposes clathrate hydrate water matrix to play the key role in selfassemblingof primary DNA molecules from nucleotide units.The experimentally observed structures of gas hydrates of cubic (‐I and ‐II) andhexagonal type belong to high symmetry groups (Pn3m, Fd3m and P6/mmm, respectively).This symmetry, however, characterizes the structure of oxygen cage but not thearrangement of the hydrogen atoms, whose actual positions are smeared by crystaldisorder.In this work, we report global lattice energy minimization results of clathrate hydratecrystals. Interactions of water molecules were modeled with the TIP4P potential set [2],which involves a 6‐12 LJ atom‐atom potential, to describe van der Waals interactions ofoxygen atoms, and electrostatic point charges accounting for the Coulomb interactions ofthe polar molecules. The water and guest methane molecules were treated as rigid bodies[3]. The starting models for minimization were built on lattice constants and oxygen atomspositions taken from experiment, while the staring sets of Euler angles were taken atrandom from the list of 1080 matrices corresponding to a nearly uniform distribution ofmolecular rotations in the three‐dimensional space. For the three structure types, thecalculations were performed in the frameworks of space group P1, assuming no crystalsymmetry except lattice translations, and centrosymmetric P‐1 group. All in all ten145