# Approximation from discrete Kronecker Delta to continuum Dirac Delta

I am working on second quantization of the Dirac field with discrete momentum I was asked to compute the creation/annihilation anticommutator by imposing the anticommutators on $$\psi$$ i.e.

$$\{\psi_a(\vec{x}),\psi^{\dagger}_b(\vec{y})\} = \delta^{(3)}(\vec{x}-\vec{y})\delta_{ab}$$

$$\psi(\vec{x}) = \sum_{r,\vec{k}} \sqrt{\dfrac{m}{VE_{\vec{k}}}}\bigg[ c_k(\vec{k})\,u_r(\vec{k}) \,e^{-i x \cdot p} + d^{\dagger}_r(\vec{k})\,v_r(\vec{k})\, e^{ix \cdot p} \bigg]$$

Since I am trying to isolate $$c$$ and $$d$$ I try to multiply for the expoencial $$e^{ix\cdot p'}$$ and integrate over the volume, and I will apear an integral like this

$$\iiint_V e^{-i \,x \cdot (p'-p)} \,d^3x$$

Is there any way approximate this? Like doing:

$$\iiint_V e^{-i \,x \cdot (p'-p)} \,d^3x \approx V\delta_{p,\,p'}$$