2) occurrence -This DF linearly penalizes non-unique molecules based on the number of previous occurrences, which acts as a more lenient version of the unique DF. The score is transformed according to the number of previous occurrences (𝐎𝐜𝐜) beyond an allowed tolerance (𝐓𝐨𝐥) until a hard threshold is reached, referred to as the buffer (𝐁𝐮𝐟𝐟). This is shown in Equation .