# Integrating Electric Displacement

Code:
Suppose the dielectric material is fixed in position and filling the capacitor, and you would have this term in the way of calculating something.

$$\int\nabla\cdot\left[\left(\Delta{D}\right){V}\right]{d}\tau$$

where D is the dielectric displacement

Now that turns into (by divergence theorem):

$$\int\left(\nabla{D}{V}\right)\cdot{d}a$$

Now my textbook says that this term would vanish if we integrate over all of space. Why is that? Thanks for your help in advance. =)