  KZnBi was discovered recently as a new three-dimensional Dirac semimetal with
a pair of bulk Dirac fermions in contrast to the $\mathbb{Z}_2$ trivial
insulator reported earlier. In order to address this discrepancy, we have
performed electronic structure and topological state analysis of KZnBi using
the local, semilocal, and hybrid exchange-correlation (XC) functionals within
the density functional theory framework. We find that various XC functionals,
including the SCAN meta-GGA and hybrid functional with 25\% Hartree-Fock (HF)
exchange (HSE06), resolve a topological nonsymmorphic insulator state with the
glide-mirror protected hourglass surface Dirac fermions. By carefully tuning
the XC strength in modified Becke-Johnson (mBJ) potential, we recover the
correct orbital ordering and Dirac semimetal state of KZnBi. We further show
that increasing the default HF exchange in hybrid functional ($> 40\%$) can
also capture the desired Dirac semimetal state with the correct orbital
ordering of KZnBi. The calculated energy dispersion and carrier velocities of
Dirac states are found to be in excellent agreement with the available
experimental results. Our results demonstrate that KZnBi is a unique
topological material where large XC effects are crucial to producing the Dirac
semimetal state.
