Structures and properties of ionic crystals and condensed phase ionic liquids predicted with the generalized energy‐based fragmentation method

The generalized energy‐based fragmentation (GEBF) approach is extended to facilitate ab initio investigations of structures, lattice energies, vibrational spectra and 1H NMR chemical shifts of ionic crystals and condensed‐phase ionic liquids (ILs) with the periodic boundary conditions (PBC). For selected periodic systems, our results demonstrate that the so‐called PBC‐GEBF approach can provide satisfactory descriptions on ground‐state energies, structures, and vibrational spectra of ionic crystals and IL crystals. The PBC‐GEBF approach is then applied to three realistic condensed phase systems. For three ionic crystals (LiCl, NaCl, and KCl), we apply the PBC‐GEBF approach with MP2 theory as well as some popular DFT methods to investigate their crystal structures and lattice energies. Our calculations indicate that the crystal structures obtained with PBC‐GEBF‐MP2/6–311 + G** are very close to the corresponding X‐ray structures, while PBC‐GEBF‐ωB97X‐D/6–311 + G** provides satisfactory prediction for crystal structures and lattice energies. For two polymorphs of [n‐C4mim][Cl] crystals, we find that the PBC‐GEBF approach at the M06‐2X/6–311 + G** level can give a satisfactory descriptions on structures and Raman spectra of these two crystals. Furthermore, for [C2mim][BF4] ILs, we demonstrate that their 1H NMR chemical shifts can be estimated from averaging over 5 typical snapshots (extracted from MD simulations) with the PBC‐GEBF approach at the B97‐2/pcSseg‐2 level. The calculated results account for the observed experimental data quite well. Therefore, we expect that the PBC‐GEBF approach, combined with various quantum chemistry methods, will become an effective tool in predicting structures and properties of ionic crystals and condensed‐phase ILs.