Civalleri, B.
Doll, K.
Zicovich-Wilson, C. M.
Ab Initio Investigation of Structure and Cohesive Energy of Crystalline Urea
The structure and cohesive energy of crystalline urea have been investigated at the ab initio level of calculation.
The performance of different Hamiltonians in dealing with a hydrogen-bonded molecular crystal as crystalline
urea is assessed. Detailed calculations carried out by adopting both HF and some of the most popular DFT
methods in solid-state chemistry are reported. Local, gradient-corrected, and hybrid functionals have been
adopted: SVWN, PW91, PBE, B3LYP, and PBE0. First, a 6-31G(d,p) basis set has been adopted, and then
the basis set dependence of computed results has been investigated at the B3LYP level. All calculations were
carried out by using a development version of the periodic ab initio code CRYSTAL06, which allows full
optimization of lattice parameters and atomic coordinates. With the 6-31G(d,p) basis set, structural features
are well reproduced by hybrid methods and GGA. LDA gives lattice parameters and hydrogen-bond distances
that are too small relative to experiment, while at the HF level the opposite trend is observed. Results show
that hybrid methods are more accurate than HF and both LDA and GGA functionals, with a trend in the
computed properties similar to that of hydrogen-bonded molecular complexes. When BSSE and ZPE are
taken into account, all methods, except LDA, give computed cohesive energies that are underestimated with
respect to the experimental sublimation enthalpy. Dispersion energy, not properly taken into account by DFT
methods, plays a crucial role. Such a deficiency also affects dramatically the computed crystalline structure,
especially when large basis sets are adopted. We show that this is an artifact due to the BSSE. Indeed, with
small basis sets the BSSE gives an extra-binding that compensates for the missing dispersion forces, thus
yielding structures in fortuitous agreement with experiment.
Ab Initio Investigation;experiment;urea;CRYSTAL;ZPE;B 3LYP level;trend;HF;LDA;PW;ab initio level;BSSE;PBE 0. First;functional;GGA;Crystalline UreaThe structure;calculation;basis sets;DFT methods;SVWN;lattice parameters
2007-01-11
https://acs.figshare.com/articles/Ab_Initio_Investigation_of_Structure_and_Cohesive_Energy_of_Crystalline_Urea/3033517

10.1021/jp065757c.s001