Help to adjust layout parameters

[CHEM_Eugene]

Hello!
I'd like to create graph similar to the picture:

My current result is:

The graph was built with ForceAtlas2 algorithm.

What I need is:
1. Assign different sizes for nodes.
2. Edges must have dirrerent length, but graph shouldn't be so expanded. My actual problem is clusters are too far each other.

Thanks for any advices!