Cluster structures were taken from Ref. 16 where they were obtained from a molecular dynamics simulation of F -in bulk water. All calculations were performed using the Fragme∩t code, 47 interfaced to Q-Chem v. 6.2. Timing data were obtained using compute nodes with two Intel Xeon CPU Max 9470 processors (26 cores each) with 128 Gb of memory. Each fragment calculation was provisioned to use 4 cores and 10 Gb of memory.