2.3 Norm descriptors proposed
The structure of ILs is the key factor to determine the properties of ionic liquid. With the HyperChem 7.0 software (http://www.hyper.com/), the ab initio method at the ST0-3G level was used to optimize the structure of cation, anion and IL. In order to clearly reflect the position relationship of atoms, the step matrix (MA, MB, MC MS ) and Euclidean space distance matrix (MD ) are expressed as follows:
In order to reveal the characters of atoms in molecules, the property matrices based on a series of atomic properties are as Eqs. (7-13):
Where,aw, mw, e, ip, r, ne, el and q represent atom weight, molecular weight, electronegativity, ionization potential, atomic radius, outermost number of electrons, number of electron layers and atom charge, respectively.
The atomic distribution matrix (M ), used for density, viscosity and thermal conductivity, are shown in Supporting Information Tables C1-C3. The M is composed of the distance matrix or the combination of step matrix and property matrix, which reflects the relationship between atoms and the special contribution of each atom. Then, the norm descriptors (I ) were calculated from the Mthrough the following formulas (Eqs. (14-17)).