Investigating 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 incorporation of growth units generally takes place on undercoordinated sites on the growing crystal facet. In this work, we use molecular 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 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 propensities. We find that the mechanism as well as the work of defect formation are markedly solvent and facet dependent. Based on Mean Force Integration and Well Tempered Metadynamics, 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 in-silico screenings of crystallization solvents

Performance of the RB3-LYP, RMP2, and UCCSD(T) procedures in calculating radical stabilization energies for •NHX radicals

N-H bond dissociation energies (BDEs) and radical stabilization energies (RSEs) associated with the •NHCF3, •NHCHO, •NHCOCH3, and •NHCONH2 radical have been calculated at a number of theoretical levels. These include UHF, RHF, UB3-LYP, RB3-LYP, UMP2, RMP2, UCCSD(T), and URCCSD(T) with a variety of basis sets, as well as the high-level composite methods W1, CBS-QB3, andG3X(MP2)-RAD. For these systems, particular care must be taken to ensure convergence to the lowest-energy solution of the self-consistent-field (SCF) equations. We have assessed the performance of the various levels of theory in calculating the BDEs and RSEs of the •NHX radicals and find that, although there are somewhat larger errors for the simpler methods, the performance generally parallels that observed previously for •CH2X radicals. In particular (and in contrast to a recent report), RB3-LYP and UCCSD(T) consistently produce very good RSEs for •NHX radicals, provided that the lowest-energy solutions are correctly identified. The RMP2 RSEs, while not as good as those for •CH2X radicals, do not show the previously claimed large errors