I'm trying to build a CNT-reinforced epoxy vitrimer composite using Amorphous Cell but consistently encountering packing failures. The goal is to pack a DGEBA/AFD polymer matrix around a centered, periodic (12,12) armchair SWCNT while excluding the CNT interior.
System Details:
CNT: (12,12) armchair, periodic, 37 repeat units, ~91 Å length
Box: 91×91×91 Å orthogonal cell
Matrix: DGEBA + AFD (2:1 molar ratio)
Forcefield: pcff_30
Materials Studio 2025
Approaches Tried:
Attempt 1: Packing with constrained CNT (no isosurface)
CNT atoms constrained (Fix Cartesian X,Y,Z)
Packing task, DGEBA/AFD only in composition
Density 0.65 g/cc, 5000 loading steps, lookahead=3, close contacts OFF
Result: SUCCESS but molecules packed inside hollow CNT core
Attempt 2: Packing with isosurface exclusion. Following advice I found in old forum threads, I implemented:
Placed dummy Ne atoms along CNT axis (X=45.5, Y=45.5, Z spacing 1.5 Å)
Generated Connolly surface (grid 0.75 Å, vdW scale 1.0, radius 1.0 Å)
Deleted Ne atoms, kept surface
Enabled "Pack in isosurface enclosed volume"
Settings: density 0.70 g/cc, 10,000 loading steps, lookahead=3, close contacts ON (vdW scale 0.95)
Result: FAILURE - acceptance ratio drops to <0.05, projected to exceed loading steps
Is there a recommended workflow for packing polymers around constrained periodic frameworks in Amorphous Cell? How do I prevent molecules from packing inside a hollow CNT while still achieving reasonable packing density? The isosurface approach seems theoretically correct but acceptance ratios are prohibitively low. Should I be using Construction task instead of Packing? If so, how do I maintain CNT position/alignment? Are there parameter combinations (density, vdW scaling, loading steps, etc.) known to work for this type of constrained geometry?
What I've Already Tried:
Densities from 0.65 to 1.16 g/cc
Loading steps from 1000 to 10,000
vdW scaling from 0.90 to 0.95
Lookahead values 1 to 3
Close contacts ON and OFF
With and without isosurface exclusion
