  A state-specific multireference coupled-cluster method based on Arponen's
bivariational principle is presented, the bivar-MRCC method. The method is
based on singlereference theory, and therefore has a relatively straightforward
formulation and modest computational complexity. The main difference from
established methods is the bivariational formulation, in which independent
parameterizations of the wavefunction (ket) and its complex conjugate (bra) are
made. Importantly, this allows manifest multiplicative separability (exact in
the extended bivar-MRECC version of the method, and approximate otherwise),
while preserving polynomial scaling of the working equations. A feature of the
bivariational principle is that the formal bra and ket references can be
included as bivariational parameters, which eliminates much of the bias towards
the formal reference. A pilot implementation is described, and extensive
benchmark calculations on several standard problems are performed. The results
from the bivar-MRCC method are comparable to established state-specific
multireference methods. Considering the relative affordability of the
bivar-MRCC method, it may become a practical tool for non-experts.
