HPC-XTB Skill

XTB (Extended Tight Binding) is a semi-empirical quantum chemistry method developed by Grimme, providing fast and reliable molecular structure and energy calculations.

Quick Start

Step	Task	Reference
1	Choose method (GFN2-xTB/GFN1-xTB/GFN-FF)	01-methods
2	Select calculation type (SP/Opt/Hess/MD)	02-calculation-types
3	Configure solvation model (GBSA)	02-solvation
4	Conformational search with CREST	03-crest
5	Conformer generation and screening	03-crest-conformer
-	Diagnose and fix runtime errors	error-recovery

Skill Map

User Requirements
├─ Energy Calculations
│  ├─ Single Point Energy → --sp
│  └─ Energy Decomposition → --pop
├─ Structure Optimization
│  ├─ Geometry Optimization → --opt
│  └─ Transition State Search → --gfnff-ts
├─ Molecular Dynamics
│  ├─ MD Simulation → --md
│  └─ Metadynamics → --metadyn
├─ Spectroscopy
│  ├─ Vibrational Spectrum → --hess
│  └─ Electronic Spectrum → --vipea
└─ Advanced Applications
   ├─ Solvation → --gbsa
   ├─ Conformational Search → --crest
   └─ ONIOM → Combine with other software

Key Decision Points

Question	Guide	Summary
Method?	01-methods	GFN2-xTB (default), GFN1-xTB, GFN-FF
Charge?	--chrg	Molecular charge
Spin?	--uhf	Open-shell systems
Solvent?	02-solvation	GBSA for solution environment
Parallel?	-P	Multi-core parallel
Precision?	--etol/--gtol	Convergence criteria

Guardrails

Must Check

• Molecular coordinates are correct (units: Angstrom)
• Charge settings are correct
• Spin settings are correct (for open-shell systems)
• Solvent model selection is reasonable
• Output files exist after calculation

Common Errors

1. SCF not converged: Increase iteration count
2. Unreasonable structure: Check initial coordinates
3. Insufficient memory: Reduce parallel processes
4. Solvent error: Check solvent name

Outputs

Always report:

• Calculation type and method (GFN2-xTB/GFN1-xTB)
• Charge and spin settings
• SCF convergence status
• Key output files (.out, .xyz, .hess)
• Total energy and optimized geometry (if applicable)

Assets

When to include: When the skill needs files that will be used in the final output.

Use cases: Templates, boilerplate code, batch scripts that get copied or modified.

File	Use Case
assets/templates/sp_xtb.sh	Single point energy calculation
assets/templates/opt_xtb.sh	Geometry optimization
assets/templates/hess_xtb.sh	Frequency calculation
assets/templates/md_xtb.sh	MD simulation
assets/templates/crest_slurm.sh	CREST conformational search

Reference Summary

All references are used in this skill:

Document	Topic
01-methods	GFN2-xTB, GFN1-xTB, GFN-FF methods
02-calculation-types	SP, Opt, Hess, MD calculation types
02-solvation	GBSA solvation model
03-crest	CREST conformational search
03-crest-conformer	Conformer generation and screening
error-recovery	SCF convergence, structure errors, memory, solvent

Error Recovery

Consult references/error-recovery.md for structured diagnosis of:

• SCF convergence failures
• Structure and coordinate errors
• Memory allocation errors
• Solvent model issues

Minimal Example

# Single point energy calculation
xtb molecule.xyz --sp

# Geometry optimization
xtb molecule.xyz --opt

# Frequency calculation
xtb molecule.xyz --hess