Total energy computations using density functional theory are typically carried out at a zero temperature; thus, entropic and thermic contributions to the total energy are neglected, even though functional materials work at finite temperatures. This book chapter investigates the Boltzmann populations of the fluxional Be6B11− and chiral Be4B8 isomers at finite temperature estimated within the framework of density functional theory, CCSD(T), and statistical thermodynamics. A couple of steps are taken into account to compute the Boltzmann populations. First, to identify a list of all possible low-energy chiral and achiral structures, an exhaustive and efficient exploration of the potential/free energy surfaces is carried out using a multi-level and multi-step global hybrid genetic algorithm search coupled with Gaussian code. Second, the thermal or so-called Boltzmann populations were computed in the framework of statistical thermodynamics for temperatures ranging from 20 to 1500 K at DFT and CCSD(T) theoretical levels. The results show the effects of temperature on the distribution of isomers define the putative global minimum at finite temperature due to the minimization of the Gibbs free energy and maximization of entropy. Additionally, we found that the fluxional Be6B11− cluster is strongly dominant at hot temperatures, whereas the chiral Be4B8 cluster is dominant at room temperature. The methodology and results show the thermal effects in the relative population hence molecular properties.
Part of the book: Density Functional Theory