Binding and excitations in Si_xH_y molecular systems using quantum Monte Carlo

Area of Science:

• Computational chemistry
• Quantum mechanics
• Materials science

Background:

• Accurate electronic structure calculations are crucial for understanding molecular properties.
• Quantum Monte Carlo (QMC) offers a powerful approach for correlated electronic structure.
• Evaluating fixed-node errors in QMC is essential for reliable predictions.

Purpose of the Study:

• To assess the accuracy of fixed-node diffusion QMC for ground and excited states of Si_xH_y systems.
• To quantify fixed-node errors using single-reference trial wave functions.
• To investigate the performance of QMC for silicon and related elements.

Main Methods:

• High-accuracy correlated calculations using Quantum Monte Carlo (QMC).
• Application of various many-body wave function approaches with basis set expansions.
• Valence-only framework utilizing correlation consistent effective core potentials.

Main Results:

• QMC atomization energies achieve high accuracy, within ≈0.07 eV of exact results.
• Fixed-node QMC biases for total energies are uniform (1–3.5%, ≤0.2 eV) across different states.
• Low fixed-node biases are observed for Si systems, suggesting similar performance for Ge, Sn, etc.

Conclusions:

• Fixed-node diffusion QMC with appropriate trial wave functions provides highly accurate results for Si_xH_y.
• The method demonstrates remarkable uniformity in energy biases across various electronic excitations.
• QMC is a reliable tool for electronic structure calculations of silicon and related main group elements.