D2BIA_discrete Model 3 - zero-cost calculation of local aromaticity index for linear acenes

D2BIA_discrete (model 3) is a zero-cost method to obtain local aromaticity of linear acenes. It has an excellent coefficient of determination (R2 above 0.92) with six-center index (SCI aromaticity index) for the group of 1-acene (benzene) to 11-acene (undecacene). However, the coefficient of determination with FLU for local aromaticity, ring by ring analysis, is poor (R2 above 0.45). Nonetheless, the metrics with SCI (R = 0.960, RMSE = 0.219, MAE = 0.139, MRE = 4.83%) are excellent. Both D2BIA_discrete and SCI have the same aromaticity gradient from terminal to center ring in linear acenes. Then, model 3 of D2BIA_discrete (whose alfa and gamma parameters were optimized and validated, ring-by-ring, using LONOCV algorithm) is a new, important tool to calculate and evaluate the local aromaticity of linear acenes in the scope of its aromaticity gradient in agreement with SCI and PDI results. This Python code allows the user to select any ring of a linear acene to obtain its D2BIA_discrete value. In addition, it also can generate the aromaticity data for all other rings of the same linear acene.