I have an Orca 5.0.3 job:
!B3LYP 6-31++G(D,P) Opt PAL3 CPCM(Water) ANFREQ
* xyz 0 1
...
The geometry optimization produced a structure at attach 1, with O16-H23 distance 2.63944, but with negative frequencies. To get rid of them, I repeated the job with these keywords:
!B3LYP 6-31++G(D,P) Opt PAL3 CPCM(Water) AnFreq
!TightOpt DefGrid3 VeryTightSCF
* xyz 0 1
...
Finally I got an optimized geometry without negative frequencies, but the structure is different - see attach 2. The distance O16-H23 is now 3.89712.
Isn't that strange that the optimized structure does not have this O:H hydrogen bond?
At attach 3 you can see one more optimized (at the same level ) structure, which seems to be ok - the O15..H21 distance is 2.27375. My intuition tells me that this is a correct calculation.
The structure from attach 1 was also computed at B3LYP-D4 level and everything seems ok - see attach 4 (O16..H23 distance is 2.21156):
!B3LYP D4 6-31++G(D,P) Opt PAL3 CPCM(Water) ANFREQ
* xyz 0 1
...
Maybe this is a bug in Orca?
Grigoriy Zhurko