Confusion regarding the usage of donors_sel, acceptors_sel and between keyword of HydrogenBondAnalysis Class.

[Sumit112192]

When I run the below two codes, they give two different results. Intuitively, the code should output the same result, so why the difference?

import numpy as np

import MDAnalysis as mda
from MDAnalysis.tests.datafiles import PSF, DCD
from MDAnalysis.analysis.hydrogenbonds import HydrogenBondAnalysis


u = mda.Universe(PSF, DCD)

hbonds = HydrogenBondAnalysis(
   universe=u,
   donors_sel="protein",
   acceptors_sel="protein"
)
hbonds.run()

for bond in hbonds.results.hbonds:
   print(bond)

import numpy as np

import MDAnalysis as mda
from MDAnalysis.tests.datafiles import PSF, DCD
from MDAnalysis.analysis.hydrogenbonds import HydrogenBondAnalysis


u = mda.Universe(PSF, DCD)

hbonds = HydrogenBondAnalysis(
    universe=u,
    between=["protein", "protein"]
)
hbonds.run()

for bond in hbonds.results.hbonds:
    print(bond)