An ab initio crystal structure prediction study, starting from gas phase optimization of the molecule at the B3LYP level, with crystal structure generation using a global search algorithm, and lattice energy minimization within an exp-6 repulsion -dispersion potential, was carried out to generate the stable lattice energy minima of 4-amino-3,5-dinitrobenzamide (DOPLOL). The hypothetical structures with favorable packing and cell volume generated from the global search were reminimizedwith a distributed multipole model of the charge density of the molecule. The possible stable polymorphs of DOPLOL from the lower energy region of the generated energy landscape plot were analyzed. The hypothetical lattice energy minimized DOPLOL structures with packing motifs and intermolecular short contacts similar to known experimental DOPLOL crystal structures were analyzed in detail to authenticate the energy landscape. Thermodynamic stability of theoretically predicted structures of DOPLOL were verified from the second derivative mechanical properties evaluated from the hessian matrix and simulated PXRD patterns were generated.
A validation study to predict the possible stable polymorphs of Pyrazinamide
within a low energy conformational region of the flexible torsion angle was
made through a potential energy surface (PES) scan by gas phase optimisation
using the MP2/6-31G(d,p) method. Hypothetical crystal structures with
favourable packing density for each of the stable conformers generated from
the PES scan were generated using a global search with a repulsion only
potential field. The densest crystal structures with stable energy were
analyzed with more accurate lattice energy minimisation via distributed
multipole analysis using a repulsion-dispersion potential. The stability of
the predicted crystal structures with similar close packing to the known
experimental polymorphs of Pyrazinamide molecule was analyzed by inspecting
their intermolecular short contacts. Studies to analyze the second derivative
mechanical properties from the hessian matrix were carried out to emphasise
the thermodynamic stability of predicted polymorphs of Pyrazinamide.
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