Table 2. Simple Analytical Functions (AF) of ν(OH) vs. Descriptor Correlation Functions Obtained from Least-Squares Fitting^a.

descriptor	figure no.	pop.	fitted function	R2 AF	RMSE AF (cm–1)	RMSE GPR (cm–1)
r(OH)	6a	H2O	ν(OH) = 28382 – 25486r(OH)	0.994	31	31
		OH–	ν(OH) = 29692 – 26838r(OH)
R(H···O)	6b	H2O	ν(OH) = 3552 – 563923 exp[−3.7427R(H···O)]	0.955	82	84
		OH–	ν(OH) = 3543 – 387690 exp[−3.6398R(H···O)]
R(O···O)	6c	H2O	ν(OH) = 3573 – 303244509 exp[−3.9096R(O···O)]	0.316	251	193
		OH–	ν(OH) = 3497 – 1119223148546828 exp[−11.0475R(O···O)]
s(OH)geom	6e	H2O	ν(OH) = 4137 – 343880 exp[−6.4849R(O···O)]	0.924	107	107
		OH–	ν(OH) = 3691 – 20747231 exp[−12.1364R(O···O)]
s(OH)QM	6f	H2O	ν(OH) = 3914 – 1777661 exp[−10.0496R(O···O)]	0.8676	136	139
		OH–	ν(OH) = 3579 – 33146109 exp[−15.0278R(O···O)]
E∥OH	6g	H2O	ν(OH) = 3622 – 196774E2 – 4240.1077E	0.941	94	92
		OH–	ν(OH) = 2986 – 254521E2 + 24325.283E
E∥H···O®	6h	H2O	ν(OH) = 3535 – 230291E2 – 2491.1702E	0.9493	86	86
		OH–	ν(OH) = 3538 – 98376E2 – 434.02758E
total E	6j	H2O	ν(OH) = 3676 – 199230E2 – 4511.8717E	0.9493	86	92
		OH–	ν(OH) = 3025 – 239817E2 + 22673.08E

^aAll quantities were obtained from our DFT calculations. The fitted parameters presented in the table are taken from one representative fit. RMSE and R² values refer to the whole combined data-set and are given in the rightmost columns. Distances are given in Å, electric fields in atomic units.