Why aren't large, low-speed propellers widely used? I am trying to calculate different propellers for the simple case like helicopter moving slow up like 1 m/s or staying/hanging in one place.

From generic physics point of view it is more efficient to push back more mass with low speed, then to push back less mass with higher speed.

Efficiency (Kg/Watt) I mean how many thrust in kg I will get from 1 Watt of power.

I did calculation using Prop selector software as shown in screenshot below big propeller 4 meters with only 32 RPM procude 1kg of thrust and power is just 13 Watts. Speed of the end of propeller will be 6.7 m/s.

Small propeller 27 cm with 7000RPM with the same 1 kg thrust needs 176 Watts of power. Speed of the end of propeller will be 99 m/s. 13 times more power!

Red thrust in the screenshot means "propeller is stalled", but maybe this "stalled" does not make sence for static case, when propeller is not moving.



My question is Why this type of propeller (big diameter, but low speed) is not in use? Is it just practical consideration like big field will be needed if I make very big propeller, or my calculation is wrong or something else?
You are not wrong, it is more efficient to accelerate a large mass by a little than a small mass by a lot.

This is due to momentum being linear with speed and mass, while energy is linear with mass but quadratic with speed, so the same momentum can be obtained more efficiently by slowly pushing a large amount of air, e.g. with a large propeller.

The reasons against this are as you imagined, like clearance from the ground and other parked craft. Also, extremely long propeller blades will suffer from high inertia and bending moments, without the benefit of centrifugal stiffness. And then there is the issue of keeping the propeller tips subsonic, to avoid wasting a lot of energy in the form of sound.