Run from the ledge into the open doorway while hitting the frozen Atomic and the door transition simultaneously, just as the Atomic thaws and touches Samus during the transition. Note that this requires a precise freeze (3 pixel window), precise thaw timing, and a 50% success rate due to collision oscillation. The starting position of Samus is a bit more lenient than other downward G-mode setups, as Samus can have higher run speed when hitting the Atomic than in most other rooms. One normalized setup to get into a usable position is to run into the right pillar, turn around, then run back.