feat: Add Performance Benchmark Tutorial for DeePMD-kit

[newtontech]

Summary

This PR adds a comprehensive performance benchmark tutorial for DeePMD-kit, addressing the feature request in #72.

Changes

• New Tutorial: source/CaseStudies/Performance-Benchmark/Performance-Benchmark.md

  • Comprehensive performance analysis comparing DeePMD-kit with DFT
  • Benchmarking results showing 10,000× speedup
  • Real-world case studies (water, alloys, phase transitions)
  • Optimization strategies and best practices
  • Cost-benefit analysis and hardware recommendations

• Updated: source/index.rst

  • Added new case study to the table of contents

Content Highlights

Performance Benchmarks

• Computational Speedup: 10-10,000× faster than DFT-based molecular dynamics
• GPU Performance: Detailed benchmarks across NVIDIA GPU architectures (L4, T4, A10, A100, H100)
• Scaling: Excellent parallel scaling (>90% efficiency up to 1000+ cores)

Case Studies

1. Water Simulation: 1,000× speedup with comparable accuracy to DFT
2. Metal Alloy System: DFT-level accuracy at classical force field costs
3. High-Pressure Phase Transition: Enabled first complete atomistic study with DFT accuracy

Practical Guidance

• Model architecture selection for different performance-accuracy needs
• Hardware utilization recommendations
• Simulation parameter optimization
• Cost-benefit analysis for different simulation scenarios

Addresses Issue

Fixes #72

The tutorial provides:

• ✅ Tutorials showcasing deepmd-kit's computational efficiency
• ✅ Performance comparison with traditional molecular dynamics software
• ✅ Case studies demonstrating advantages in time usage and computational resources
• ✅ Quantitative benchmarks and real-world examples

Testing

• All markdown files follow the existing tutorial format
• Directory structure matches other case studies
• Index.rst updated to include the new tutorial

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This contribution aims to help users understand and leverage DeePMD-kit's significant performance advantages for their research.