  We introduce a half-filled Hamiltonian of spin-half lattice fermions that can
be studied with the efficient meron-cluster algorithm in any dimension. As with
the usual bipartite half-filled Hubbard models, the na\"ive $U(2)$ symmetry is
enhanced to $SO(4)$. On the other hand our model has a novel spin-charge flip
${\mathbb Z}^C_2$ symmetry which is an important ingredient of free massless
fermions. In this work we focus on one spatial dimension, and show that our
model can be viewed as a lattice-regularized two-flavor chiral-mass Gross-Neveu
model. Our model remains solvable in the presence of the Hubbard coupling $U$,
which maps to a combination of Gross-Neveu and Thirring couplings in one
dimension. Using the meron-cluster algorithm we find that the ground state of
our model is a valence bond solid when $U=0$. From our field theory analysis,
we argue that the valence bond solid forms inevitably because of an interesting
frustration between spin and charge sectors in the renormalization group flow
enforced by the ${\mathbb Z}^C_2$ symmetry. This state spontaneously breaks
translation symmetry by one lattice unit, which can be identified with a
$\mathbb{Z}_2^\chi$ chiral symmetry in the continuum. We show that increasing
$U$ induces a quantum phase transition to a critical phase described by the
$SU(2)_1$ Wess-Zumino-Witten theory. The quantum critical point between these
two phases is known to exhibit a novel symmetry enhancement between spin and
dimer. Here we verify the scaling relations of these correlation functions near
the critical point numerically. Our study opens up the exciting possibility of
numerical access to similar novel phase transitions in higher dimensions in
fermionic lattice models using the meron-cluster algorithm.
