In the test case "Truncated-Octahedron," where ehal is tapered off at 7 angstroms. The distance of this pair in double-precision is 6.999999569589844. With some machine/GPU/compiler combinations, the single-precision distance is rounded to 7.0 angstroms, making the tapered pairwise VDW energy to 0. Therefore, this pair will be excluded from the VDW counts.
https://github.com/TinkerTools/tinker9/blob/0e8720f08608ebd8fbbd108b54cbc195314e0e53/src/test/file/trunc8/arbox.xyz#L128 https://github.com/TinkerTools/tinker9/blob/0e8720f08608ebd8fbbd108b54cbc195314e0e53/src/test/file/trunc8/arbox.xyz#L200
In the test case "Truncated-Octahedron," where ehal is tapered off at 7 angstroms. The distance of this pair in double-precision is 6.999999569589844. With some machine/GPU/compiler combinations, the single-precision distance is rounded to 7.0 angstroms, making the tapered pairwise VDW energy to 0. Therefore, this pair will be excluded from the VDW counts.