Z k,11 ∆u k,1 . The sum runs over all the atom in the simulation cell; A is the area of the cell and e is charge of an electron. We use mean BECs (Z k,11 ) i. BECs have been observed for other well known ferroelectric materials . In agreement with previous reports, we nd that MOX 2 monolayers have quite large P 1 , which is comparable with that of group-IV monochalcogenide orthorhombic monolayers, e.g., SnS . We also estimate the energy barrier for FE polarization switching. We take the dierence in energy (∆E) between FE and PE phases; lattice parameters a and b are fully relaxed for both phases. Our ∆E values are in good agreement with the reported values. We see a general trend that P 1 , ∆E, and iω Γ decrease as ionic radius of X increases from F to Br. Interestingly, we also observe that magnetic VOX 2 monolayers have signicantly larger P 1 than non-magnetic TiOCl 2 or TiOBr 2 . This is in line with the previous report that presence of an electron in d xy orbital of V does not suppress rather enhances ferroelectric polarization. This is also conrmed by larger iω Γ of VOX 2 (see Table ). We consider four (1 FM and 3 AFM) collinear magnetic congurations (see Figure )) for VOX 2 monolayers. Each V 4+ contributes 1 µ B , which comes from an unpaired electron in d xy orbital. Comparing the energy of a conguration with respect to FM order, in agreement with previous reports, we nd that FE VOF 2 monolayer has FM groundsate . However, we nd that AFM1type AFM order is more stable than other congurations in VOCl 2 and VOBr 2 monolayers . By applying an external magnetic eld, AFM1 order can be changed to FM. This will also lead a change in P 1 about 7.49% and 6.13% reduction for VOCl 2 and VOBr 2 monolayers, respectively. AFM1-to-FM transition slightly hardens the soft mode (iω Γ ; see Table ), consequently reduces the ferroelectric switching barrier (ΔE ) slightly. This indicates that there is a weak coupling between magnetic and ferroelectric order in VOX 2 .