Infrared spectra of amorphous and crystalline urea ices

Infrared spectra of amorphous urea and urea:H2O ices between 30 K and 270 K are provided to guide astrophysical searchers. Density Functional Theoretical calculations of the spectra of crystalline and amorphous samples agree well with experiment.

Controlling the aqueous growth of urea crystals with different growth inhibitors: a molecular-scale study

Effect of different growth additives on the aqueous growth of crystalline urea is investigated computationally at the different levels of supersaturation and additive concentration.

Can We Predict the Pressure Induced Phase Transition of Urea? Application of Quantum Molecular Dynamics

Crystalline urea undergoes polymorphic phase transition induced by high pressure. Form I, which is the most stable form at normal conditions and Form IV, which is the most stable form at 3.10 GPa, not only crystallize in various crystal systems but also differ significantly in the unit cell dimensions. The aim of this study was to determine if it is possible to predict polymorphic phase transitions by optimizing Form I at high pressure and Form IV at low pressure. To achieve this aim, a large number of periodic density functional theory (DFT) calculations were performed using CASTEP. After geometry optimization of Form IV at 0 GPa Form I was obtained, performing energy minimization of Form I at high pressure did not result in Form IV. However, employing quantum molecular isothermal–isobaric (NPT) dynamics calculations enabled to accurately predict this high-pressure transformation. This study shows the potential of different approaches in predicting the polymorphic phase transition and points to the key factors that are necessary to achieve the success.

The applicability of the dimeric heterosynthon concept to molecules with equivalent binding sites. A DFT study of crystalline urea–H2O2

The limited applicability of the dimeric heterosynthon concept to a two-component urea–H2O2crystal is reported.