We virtually screen 41 different substituents and 7 possible substituent positions (Figure ) of the dihydroazulene/vinylheptafulvene (DHA/VHF) thermal heat battery (Figure ) for molecules with high storage density (∆H • rxn /MW) and stability (∆G •, ‡ ) The size of the chemical space is roughly 230 billion molecules. We start by screening all 35,588 singly and doubly substituted DHAs using semiempirical methods (SQM): GFN2-xTB for the storage density and PM3 for the barrier height of the back reaction. Compared to M06-2X/6-31G(d), PM3 tends to significantly overestimate the barrier relative to the reference compound, while GFN2-xTB tends somewhat underestimate the storage energy, but the methods are sufficiently accurate to identify promising molecules for further refinement (Figure ).