Figure 1. The comparison of leave-one-out cross-validation
(LOO-CV) and leave-one-ion-out
cross-validation (LOIO-CV) methods: orange ball with
Ci stands
for cations, blue ball with Ai stands for anions
and Ci tightly close to the
Ai stand for ILs, and the balls in different
shades with fk (T ,P ) represent data
points at variable temperatures and pressure.
Other validation protocols. The correlation coefficient
(R 2) and mean absolute error (MAE) were used to
evaluate the QSPR model quantitatively35. The
definitions of these parameters are listed in Table S1 of Supporting
Information (Statistical parameters.docx). Through external validation,
the predicting ability of these models was fully evaluated byR 2training of the training set
and R 2testing of the testing
set. To avoid cations and anions in the testing set reappearing in the
training set in the meantime, the dataset was divided into training set
(80%) and testing set (20%) by the ion structures and the proportion
of data points. Y -randomization test was used to avoid the
possibility of chance correlation in modeling36.