  Excess work is a non-diverging part of the work during transition between
nonequilibrium steady states (NESSs). It is a central quantity in the steady
state thermodynamics (SST), which is a candidate for nonequilibrium
thermodynamics theory. We derive an expression of excess work during
quasistatic transitions between NESSs by using the macroscopic linear response
relation of NESS. This expression is a line integral of a vector potential in
the space of control parameters. We show a relationship between the vector
potential and the response function of NESS, and thus obtain a relationship
between the SST and a macroscopic quantity. We also connect the macroscopic
formulation to microscopic physics through a microscopic expression of the
nonequilibrium response function, which gives a result consistent with the
previous studies.
