  We analytically study the quantum phase diagrams of ultracold dipolar Bose
gases in an optical square lattice at zero temperature by using the generalized
effective-potential Landau theory (GEPLT). For a weak nearest-neighbor
repulsion, our analytical results are better than the third-order
strong-coupling expansion theory calculation [M. Iskin et al.,
\textcolor[rgb]{0.00,0.00,1.00}{ Phys. Rev. A \textbf{79}, 053634 (2009)}]. In
contrast to a previous quantum Monte Carlo (QMC) simulation [T. Ohgoe et al.,
\textcolor[rgb]{0.00,0.00,1.00}{Phys. Rev. B \textbf{86}, 054520 (2012)}], we
analytically calculate phase transition boundaries up to the third-order
hopping, which are in excellent agreement with QMC simulations for second-order
phase transition.
