  A modified lattice Boltzmann model with multiple relaxation times (MRT) for
the convection-diffusion equation (CDE) is proposed. By modifying the
relaxation matrix, as well as choosing the corresponding equilibrium
distribution function properly, the present model can recover the CDE with
anisotropic diffusion coefficient with no deviation term even when the velocity
vector varies generally with space or time through the Chapman-Enskog analysis.
This model is firstly validated by simulating the diffusion of a Gaussian hill,
which demonstrates it can handle the anisotropic diffusion problem correctly.
Then it is adopted to calculate the longitudinal dispersion coefficient of the
Taylor-Aris dispersion. Numerical results show that the present model can
further reduce the numerical error under the condition of non-zero velocity
vector, especially when the dimensionless relaxation time is relatively large.
