Choosing a capacitor capacitance for a quartz resonator (ATMEGA328P)
A 12 pF capacitor from each side of the crystal to ground will work just fine.

So like this:



C1 and C2 need to have a certain value (each capacitor being between 5 pF and 50 pF is normal) to make the oscillator work.

Use the wrong value capacitor and the oscillator circuit will not work reliably.

The only reason to change the values of the capacitors is if you need to make the oscillator work at a very precise frequency like 16.000000 MHz.

Then normally a trimmer 1 pf to 22 pF capacitor:



is used in parallel with the crystal.

But chances are that you don't need this.

The microcontroller doesn't care about the exact frequency of the crystal oscillator. The frequency you get when using 2 x 12 pF will be more than accurate enough for almost any purpose. Only if you're building a clock you might worry about this.

There is no need to use smaller capacitors, you will only increase the chance that the oscillator will stop working!

Also there is no need to worry about the ESR of the capacitors, any modern capacitor should just work.

So: just use two 12 pF capacitors connected like shown above, and stop worrying about this :-)