Diffusion Monte Carlo calculations for all the deuterated H-7(+) isotopologues and isotopomers were performed to determine their zero-point energies, and thus the stability of them. Based on these calculations, we conclude that the deuterium atom prefers the unbonded position in the central H-3(+), and then the bonded position in H-3(+). When two deuterium atoms are in the outer H-2 units, forming a D-2 is more stable than one deuterium in each H-2 unit. We also discovered that some unstable isotopomers can rearrange to a more stable isotopomer through two types of isomerization: one is that a new H-3(+) core is formed with more deuterium atoms in it; the other is that the deuterium in the central H-3(+) goes from the interior (the bonded position) to the exterior (the unbonded position) while the number of deuterium atoms in the H-3(+) does not change. Three transition states related to the isomerization were identified, two of which have not been reported previously. The corresponding reaction paths were also determined.