Advice for setting up attraction potential measurement between 2 collagen triple helices

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GROMACS version: 2024.2
GROMACS modification: No

Greetings.

Currently, I am struggling to measure Coulombic and LJ attraction between 2 truncated Human Collagen I triple helices, whose center of mass are placed 15 Angstrom apart in z direction. My current plan for production run is to

  1. Place 1kJ/mol restraint on both molecules in all direction
  2. Enforce rotation on one molecule at constant angular velocity
  3. Run and record the result until 360 degree rotation is completed. Then observe close range LJ and Coulomb between helices

These are the dimensions of the system
Box :240 x 8 x 8 nm
Collagen Helix: 3 Alpha Chains. 240 nm long, 1.5 nm diameter triple helix

I am currently struggling with the NPT equlibration step. Where the system does not equilbrate well, and the density plot experiencs uniformly downward drift along the 10ns run. Is there any advice to improve my scheme?