ИСТИНА

It became a common place to treat crystalline solids with help of plane waves and density functionals in that or other way substantiating these moves be invoking Bloch and Hohenberg-Kohn-Sham theorems. This decouples the area of crystalline solids from say that of similarly designed glasses and requires additional work to restore or extract chemical information from such calculations. Moreover, from the point of view of this standard approach structural changes leading even to slightest variations of crystal symmetry require a separate consideration since the space group, Brillouin zone, Bloch suns and states etc are completely different despite the fact that different polymorphs may be very close chemically. The present author always says that whatever theorem is not a sentence rather an option, and it is a matter of the free will of a free and open minded researcher to chose and to apply suitable ones. In the present talk we exemplify this point by constructing analytical theory of the phase diagram of ices (solid water) valid in the pressure range up to 100 GPa (ice X) and embracing the low-pressure ices. This theory is based on the simple picture of hydrogen bonds effectively interacting through the hybridized atomic orbitals of the oxygen atoms they are incident to. By this (i) a uniform description of the low-pressure molecular and high pressure ionic ice X is achieved; (ii) the stability boundary of ice X vs transition to "molecular" ices VII and VIII and the intimate nature of its instability is clarified; (iii) the unique curvilinear form of the order/disorder phase boundary between ices VII and VIII is reproduced and understood; (iv) the low-pressure region of the phase diagram is shown to be tentatively reproducible with use of global structure variables. An excursion to the TPa pressure diapason is undertaken as well.