  We present a methodology for computing the current-voltage response of a
molecular wire within the Landauer-Buttiker formalism based upon transforming
the cummulative transmission probability into an eigenvalue problem. The method
is extremely simple to apply since does not involve construction of the
molecular Greens function, and hence avoids the use of complex integration
contours to avoid poles. We use this method to study the effect of base-pair
sequence on the conductivity of holes in DNA chains containing A-T bridges
between guanine chains. Our results indicate that sequence plays a substantial
role in ballistic transport via tunneling resonances tuned by sequence and
interchain interactions. We also find that ballistic transport is dominated by
intrachain transport and that hole transmission is insensitive to interchain
fluctuations.
