  When QCD is described by a nonrelativistic effective field theory, operators
consisting of gluonic correlators of two chromoelectric or -magnetic fields
will often appear in descriptions of quarkonium physics. At zero T, these
correlators give the masses of gluelumps and the moments of these correlators
can be used to understand the inclusive P-wave decay of quarkonium. At finite T
these correlators define the diffusion of the heavy quarkonium. However, these
correlators come with a divergent term in lattice spacing which needs to be
taken care of. We inspect these correlators in pure gauge theory with gradient
flow smearing, which should allow us to reduce and remove the divergence more
carefully. In these proceedings, we focus on the effect of gradient flow to
these correlators and the reduction of this divergence.
