usability - Minimum distance between click targets

What is the minimum distance between click targets on web for an optimal UX?

I have read this article: An Interactive Visualisation of Fitts's Law

Here is a menu with items I'm trying to position in the best way:

According to the Fitts's Law the smaller distance is the better. So if I make the distance smaller it will be less difficult to hit it, but with small distance between two items I can miss and click accidentally the other one.

So applying Fitts's Law in this case could make users miss the targets.

Is the any formula that takes into accounting, let's say, MD variable (minimum distance to not click accidentally other closely existing target)?

Answer

Distance between targets can be next to zero. Like in the menu you have. What you are missing here is the size of the target. It is easier to miss the target if it is too small. As from the image of Fitts's law you posted:

From this formula we can see that the task gets harder, the farther away the target is and the smaller it is.