Fig. 3. (a) The fragment of erlotinib used to calculate the potential energy surface. Truncated groups are shown in grey. (b) Representative solution conformations of erlotinib for the CGenFF MM model (green) and NNP/MM model (red) overlaid with the ligand pose from the 4HJO crystal structure. (c) The relaxed potential energy surfaces for rotation around the erlotinib fragment amine bonds calculated using (i) DLPNO-CCSD/def2-TZVP//MP2/def2-TZVP (ii) NNP(ANI-1ccX) and (iii) the CGenFF MM model. Energies are in kcal mol⁻¹.