The Onsager reaction-field (ORF) theory is extended to apply to three-dimensional Bravais lattices with a basis. The ORF calculation is used to predict the critical temperature for classical Ising, XY, and Heisenberg magnetic models, in particular, on diamond and hexagonal close packed lattices. Results are compared with series extrapolations and other theoretical approaches where available. Fo...

The crystal structures of piperazine, piperidine and morpholine have been determined at 150 K. All three structures are characterized by the formation of NH...N hydrogen-bonded chains. In piperazine these are linked to form sheets, but the chains are shifted so that the molecules interleave. In morpholine there are in addition weak CH...O interactions. Topological analyses show that these three...

The propagation of shock waves through polycrystalline iron is explored by large-scale atomistic simulations. For large enough shock strengths the passage of the wave causes the body-centered-cubic phase to transform into a close-packed phase with most structure being isotropic hexagonal-close-packed (hcp) and, depending on shock strength and grain orientation, some fraction of face-centered-cu...

The vibration-rotation states of a tetrahedral molecule in a field of D3h symmetry are studied by an extended group theory. Symmetry adapted rotational wave functions for the ground and the triply degenerate excited vibrational states are constructed. The crystal field potential is derived explicitly for a tetrahedral molecule in a hexagonal close-packed crystal. As an example, the rovibrationa...

Materials with a hexagonal close-packed (hcp) crystal structure such as Mg, Ti and Zr are being used in the transportation, aerospace and nuclear industry, respectively. Material strength and formability are critical qualities for shaping these materials into parts and a pervasive deformation mechanism that significantly affects their formability is deformation twinning. The interaction between...

We have investigated twin boundaries in double-lattice hexagonal close-packed metallic materials, focusing on their atomic geometry. Combining accurate ab-initio methods and large-scale atomistic simulations we address the following two fundamental questions: (i) What are the possible intrinsic twin boundary structures in hcp crystals? (ii) Are these structures stable against small distortions?...

The design of crystalline polymers is intellectually stimulating and synthetically challenging, especially when the polymerization of any monomer occurs in a linear dimension. Such linear growth often leads to entropically driven chain entanglements and thus is detrimental to attempts to realize the full potential of conjugated molecular structures. Here we report the polymerization of two-mono...

Close-packed metal surfaces and heteroepitaxial systems frequently display a structure consisting of regularly spaced misfit dislocations, with a network of domain walls separating face-centered cubic (fcc) and hexagonal close-packed (hcp) domains. These structures can serve as templates for growing regularly spaced arrays of nanoislands. We present a theoretical investigation of the factors co...

Lipids that are found in cell membranes form a variety of self-assembled phases in the presence of water. Many of these structures are liquid-crystalline with structural motifs mirrored in cells and organelles and can be exploited in the delivery of drugs and genes. We report the discovery of a lyotropic liquid crystalline phase based on a 3-D hexagonal close-packed arrangement of inverse micel...

We report here the compositional dependency of face-centered cubic (FCC) to hexagonal close-packed (HCP) martensitic transformation in FeMnCo medium entropy alloys (MEAs) and insights into underlying mechanisms. To this end, we designed MEAs with same Fe-to-Mn ratio explored phase stability therein. Higher Co content was found facilitate FCC-HCP kinetics. In situ electron backscatter diffractio...