Molecule Generative Models. In molecule generation, a generative model M encodes the molecular graph X as a latent vector Z ∈ R l with l being the latent space dimension, and further decodes latent vector back to the molecular space. Specifically, variational auto-encoder (VAE) and flow-based model (Flow) are the two most commonly used models for molecule generation, which typically encode the data from molecular space to latent space of Gaussian distribution. The encoding and decoding process can be formulated as: