Dipolar host guest interactions and geometrical confinement at the basis of the stability of one-dimensional ice in zeolite bikitaite

One-dimensional chains of hydrogen-bonded water molecules are hosted in the noncrossing channels of bikitaite (Li-2[Al2Si4O12]. 2H(2)O), a rare natural lithium zeolite [C. S. Hurlbut, Jr, Am. Mineral. 42, 792 (1957); Stahl et al., Zeolites 9, 303 (1989)]. We use first-principles methods to study such a mineral with different (Si, Al) ordering in the zeolite framework. The one-dimensional polymer of nondiffusing water molecules, one chain per channel, is arranged in such a way as to develop a permanent polarization parallel to the zeolite channel. We found that the one-dimensional and entropically unfavored water chain structure is stabilized by dipolar host/guest interactions between the dipolar water chain and the (reversed sign) dipolar framework. A ditrigonal distortion of the hexagonal arrangement of tetrahedra in the aluminosilicate bikitaite structure is probably at the origin of the net polarization of the framework, and is induced by the small-sized Li+ cations. (C) 1999 American Institute of Physics. [S0021-9606(99)70825-1].