Nanotube Generation

Overview

Nanotubes are formed by rolling a 2D sheet into a cylinder defined by chiral indices (n, m). The chirality determines electronic and mechanical properties.

Common applications:

• Carbon nanotubes (CNTs): electronics, composites, catalysis
• Boron nitride nanotubes (BNNTs): high-temperature insulation, radiation shielding
• MoS2 / WS2 nanotubes: lubricants, batteries, photocatalysis
• Custom 2D roll-ups: any 2D material loaded in the viewer

Chirality Quick Reference

Type	Condition	Electronic Character (CNT)
Armchair	n = m	Metallic
Zigzag	m = 0	Metallic if n mod 3 = 0, else semiconducting
Chiral	n != m, m != 0	Metallic if (n - m) mod 3 = 0, else semiconducting

MCP Tools

catgo_nanotube_info -- Query geometry before building

{"tool": "catgo_nanotube_info", "arguments": {
  "n": 10, "m": 0,
  "bond_length": 1.42
}}

Returns diameter, circumference, chiral angle, translational vector length, and estimated atom count without building the structure. Use this to check size before committing to a build.

catgo_nanotube_build -- Build the nanotube

{"tool": "catgo_nanotube_build", "arguments": {
  "n": 10, "m": 0,
  "length": 20.0,
  "bond_length": 1.42
}}

Parameter	Description	Default
n, m	Chiral indices	(required)
length	Tube length in Angstroms	one translational period
bond_length	C-C bond length in Angstroms	1.42

The tool accepts either a loaded 2D structure from the viewer or explicit lattice vectors / basis coordinates. For carbon nanotubes, the default graphene sheet is used automatically.

Router: /nanotube/info (POST), /nanotube/build (POST)

Complete Workflow: (10,0) Zigzag CNT Relaxation

Step 1: Check nanotube geometry

{"tool": "catgo_nanotube_info", "arguments": {
  "n": 10, "m": 0
}}

Verify the diameter (~7.8 A) and atom count are reasonable for DFT.

Step 2: Build the nanotube

{"tool": "catgo_nanotube_build", "arguments": {
  "n": 10, "m": 0,
  "length": 12.5
}}

Step 3: Verify in viewer

{"tool": "catgo_view", "arguments": {"action": "get_state"}}

Check: cylindrical geometry, no overlapping atoms, correct atom count.

Step 4: Relax with DFT

{"tool": "catgo_workflow_engine", "arguments": {
  "action": "create", "params": {"name": "(10,0) CNT relaxation"}
}}

{"tool": "catgo_workflow_engine", "arguments": {
  "action": "add_task", "params": {
    "workflow_id": "<wf_id>",
    "task_type": "geo_opt",
    "params": {"software": "vasp", "ENCUT": 520, "ISPIN": 1,
               "system_name": "CNT-10-0 relax"}
  }
}}

Multi-walled Nanotubes (MWNT)

The backend supports multi-walled nanotubes via additional walls. Each wall is defined by its own chiral indices. The inter-wall spacing defaults to ~3.4 A (van der Waals distance for graphitic layers).

Non-Carbon Nanotubes

To build a BN nanotube or MoS2 nanotube:

1. Fetch or load the 2D monolayer structure (e.g., hexagonal BN)
2. The nanotube builder rolls up whatever 2D structure is loaded

{"tool": "catgo_fetch", "arguments": {
  "action": "crystal", "formula": "BN", "source": "mc3d"
}}

Then build the nanotube from the loaded structure.

Common Pitfalls

1. Large chiral indices (n > 30) produce structures with thousands of atoms. Check atom count with catgo_nanotube_info before building.
2. The tube length should be at least one translational period for meaningful periodic calculations.
3. For DFT on nanotubes, ensure sufficient vacuum in the non-periodic directions (at least 12-15 A between periodic images).
4. Bond length 1.42 A is for graphene/CNT. Use 1.45 A for BN, 2.42 A for MoS2.
5. Semiconducting CNTs require careful k-point sampling along the tube axis. Use at least 1x1x8 k-points for a single unit cell.