Related Experiment Videos
Bond breaking with auxiliary-field quantum Monte Carlo
W A Al-Saidi1, Shiwei Zhang, Henry Krakauer
1Department of Physics, College of William and Mary, Williamsburg, VA 23187-8795, USA. al-saidi@cornell.edu
The Journal of Chemical Physics
|October 16, 2007
Summary
The phaseless auxiliary-field quantum Monte Carlo (AF QMC) method accurately maps molecular potential-energy curves during bond stretching. This advanced computational method offers improved accuracy over traditional techniques for studying electron correlation in molecules.
Area of Science:
- Computational Chemistry
- Quantum Many-Body Physics
- Materials Science
Background:
- Bond stretching in molecules is a critical benchmark for computational chemistry methods.
- Accurately describing electron correlation is essential for predicting molecular behavior.
- Approximate many-body methods require rigorous testing for reliability.
Purpose of the Study:
- To evaluate the performance of the phaseless auxiliary-field quantum Monte Carlo (AF QMC) method for bond stretching.
- To compare AF QMC with established methods like coupled cluster CCSD(T).
- To investigate the impact of different trial wave functions on AF QMC accuracy.
Main Methods:
- Utilized the phaseless auxiliary-field quantum Monte Carlo (AF QMC) method.
- Applied the method to bond stretching in BH, N(2), and H(50) systems.
- Employed unrestricted Hartree-Fock and multiconfiguration self-consistent-field wave functions as trial states.
Main Results:
- Phaseless AF QMC demonstrated superior accuracy and uniformity compared to CCSD(T) for potential-energy curves.
- The method effectively controlled the sign/phase problem in quantum Monte Carlo simulations.
- Using multideterminant trial wave functions yielded excellent results across the entire dissociation spectrum.
Conclusions:
- The phaseless AF QMC method is a robust and accurate tool for studying molecular bond stretching.
- It provides a reliable approach for investigating electron correlation effects.
- The choice of trial wave function significantly influences the accuracy and computational cost.
Related Concept Videos
02:32Bonding in Metals
Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Drüde called the “Electron Sea Model”.
02:40MO Theory and Covalent Bonding
The molecular orbital theory describes the distribution of electrons in molecules in a manner similar to the distribution of electrons in atomic orbitals. The region of space in which a valence electron in a molecule is likely to be found is called a molecular orbital. Mathematically, the linear combination of atomic orbitals (LCAO) generates molecular orbitals. Combinations of in-phase atomic orbital wave functions result in regions with a high probability of electron density, while...
01:17Spin–Spin Coupling: One-Bond Coupling
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
03:51Molecular Orbital Theory II
Molecular Orbital Energy Diagrams
02:13Bond Dissociation Energy and Activation Energy
Bond energy is the energy required to break a bond homolytically. These values are usually expressed in units of kcal/mol or kJ/mol and are referred to as bond dissociation energies when given for specific bonds or average bond energies when indicated for a given type of bond over many compounds. Firstly, the bond dissociation energy for a single bond is weaker than that of a double bond, which in turn is weaker than that of a triple bond. Secondly, hydrogen forms relatively strong bonds with...
01:20Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...