Assessment of Density Functional Approaches for Carbon Dioxide Dimerization and Solid-State Properties

We investigated the performance of various exchange-correlation functionals implemented in SIESTA, including van der Waals (vdW) dispersion corrections, specifically the (i) BH, (ii) C09, (iii) KBM, (iv) LMKLL, and (v) VV variants, as well as the generalized gradient approximation (GGA), to describe the interactions of CO₂ homodimers using density functional theory (DFT). To the best of our knowledge, the application of these functionals to CO₂ systems has not been previously reported in the literature. Accordingly, we calculated the interaction energies of the CO₂ homodimers, their vibrational modes, and the solid-phase properties using vdW-DF3-type functionals. Among the dimer configurations analyzed, the T-shaped (TS) and parallel-displaced (PD) geometries were identified as the most stable. Notably, the qualitative and quantitative behavior of the vdW-DF-C09 functional for the PD configuration showed excellent agreement with results obtained from high-level CCSD-(T)/SAPT calculations. Furthermore, vdW-DF-C09 successfully reproduced experimental data for the solid phase of CO₂, including its symmetric, asymmetric, and bending vibrational modes. A comparative analysis of different van der Waals (vdW) functionals offers valuable insights for parametrizing force fields suitable for classical simulations. These findings provide a reliable benchmark for CO₂-CO₂ interactions and may serve as a reference for future force-field development and multiscale modeling studies.