Based on the HB geometry-dependent model's ability to recapitulate the nitrile DFT frequencies, we sought to test the model by comparing predicted blueshifts against experimental data for cases with nitriles in H-bonded environments. Towards this goal, we revisited our recent work, in which we introduced the noncanonical amino acid oCNF into photoactive yellow protein (PYP). In this previous work, oCNF was incorporated into PYP in place of endogenous phenylalanines (F), resulting in two PYP variants, F92oCNF and F28oCNF, which were H-bonded and showed distinct ∆𝜈̅ 𝐻𝐵 values with moderate to large magnitudes. In the following, we reanalyze our previously obtained data (namely, IR spectra, crystal structures, and MD simulations) to enable comparisons between experimentally derived HB blueshifts (∆𝜈̅ 𝐻𝐵,𝑜𝑏𝑠 ) and HB blueshifts predicted from MD simulations using eq. 7 (i.e., ∆𝜈̅ 𝐻𝐵, (𝑑, 𝜃)). Starting with F92oCNF (Fig. ), x-ray crystallography showed that the C≡N group is engaged in a head-on HB with the hydroxyl group of threonine 90 (T90), and 100 ns long AMOEBA MD simulations indicated an average C≡N---HO-T90 HB distance and angle of 2.93 Å and 169°, respectively (see Fig. , a representative MD snapshot). Using the HB geometry-dependent model in eq. 7, we derive an average predicted value of 〈∆𝜈̅ 𝐻𝐵, (𝑑, 𝜃)〉 = 27.3 cm -1 , a large value as expected for a head-on HB (Fig. ). To compare this value to experimental results (Fig. ), we also determined the C≡N's peak position due to the VSE alone (eq. 1b); this was done by using the experimentallydetermined zero-field frequency and Stark tuning rate and the average electric field for the H-bonding fraction from MD (-78 MV/cm, ref. ; see SI Section 9 for further details). We obtain a VSE-based vibrational frequency of 2215.5 cm -1 (blue values in Fig. /Fig. and vertical blue line in Fig. ). The experimental IR spectrum of F92oCNF has a peak position of 2241.3 cm -1 , and subtracting the frequency for the VSE alone from the experimental frequency results in a HB blueshift of ∆𝜈̅ 𝐻𝐵,𝑜𝑏𝑠 = 25.8 cm -1 (eq. 2). This experimentally derived blueshift matches very well with the HB geometry-based value of 27.2 cm -1 , as indicated by the similar length of the solid and dashed double headed arrows in Fig. . We note that similar results are obtained when 〈∆𝜈̅ 𝐻𝐵, (𝑑, 𝜃)〉 is calculated from the distribution of ∆𝜈̅ 𝐻𝐵, (𝑑, 𝜃) values obtained by applying eq. 7 to each Hbonding frame of the MD simulation (see distributions for this and the following cases in Fig. ).