  The external-field method has been used extensively in the QCD sum-rule
approach to explore various hadron static properties. In the traditional
formalism of this method, the transitions from the ground state hadron to
excited states are not exponentially suppressed relative to the ground state
term and thus contaminate the ground state hadron property to be extracted. In
this paper, we suggest a modified formalism, in which the transition terms are
exponentially suppressed relative to the ground state term. As such, the pole
plus continuum spectral model, traditionally invoked in QCD sum-rule approach,
can be adopted. Thus, this modified formalism has potential to improve the
predictability and reliability of external-field sum-rule calculations, which
is illustrated in an explicit example.
