On the Role of Solvent in the Formation of Vacancies on Ibuprofen Crystal Facets

Surface defects play a crucial role in the process of crystal growth, as the incorporation of growth units generally takes place on under-coordinated sites on the growing crystal facet. In this work, we use molecular dynamics simulations to obtain information on the role of the solvent in the roughening of three morphologically-relevant crystal faces of form I of racemic ibuprofen. To this aim, we devise a computational strategy based on combining independent Well Tempered Metadynamics with Mean Force Integration. This approach enables us to evaluate the energetic cost associated with the formation of a surface vacancy for a set of ten solvents, covering a range of polarities and hydrogen-bonding ability. We find that both the mechanism of defect formation on these facets and the work associated with the process are indeed markedly solvent-dependent. The methodology developed in this work has been designed with the aim of capturing solvent effects at the atomistic scale while maintaining the computational efficiency necessary for implementation in high-throughput computational screenings of crystallization solvents.

Mechanism of Defect Formation in Zr1 – xVxNiSn Thermoelectric Material

Crystal and electronic structure, transport and energy state characteristics of the Zr1−xVx NiSn (0.01 ≤ x ≤ 0.1) thermoelectric material are investigated in the 80–400 K temperature interval. A mechanism of simultaneous generation of structural defects of the acceptor and donor nature, which determines the electric conductivity of the material, is established. It is shown that energetically expedient is a simultaneous occupation of the 4c position of Ni (3d84s2) atoms by V (3d34s2) atoms, which generates structural defects of the acceptor nature and the impurity acceptor band Ꜫ1A, as well as the 4a position of Zr (4d25s2) atoms, generating structural defects of the donor nature and the impurity donor band Ꜫ2D.