Potential Energy Curves and Excited States of the C$_2$ Molecule by Auxiliary-Field Quantum Monte Carlo (AFQMC)
ORAL
Abstract
The accurate determination of potential energy curves (PECs) and excited states represents two difficult problems in electronic structure calculations. We present AFQMC PECs of the challenging C$_2$ molecule, focusing on the ground state and two singlet low-lying excited states. AFQMC calculates a target many-body wave function (WF) by means of random walks in the space of Slater determinants. We employ truncated complete active space (CAS) trial WFs ($\Psi_T$) to guide the AFQMC projection to obtain the desired state. With the phase-free constraint,\footnote{S. Zhang and H. Krakauer, Phys. Rev. Lett. \textbf{90}, 136401 (2003)} the CAS $\Psi_T$ is effective in controlling the sign/phase problem, and filtering in the desired excited state. The AFQMC results are in very good agreement with exact results. Comparison with experimental spectroscopic constants will also be presented.
*Supported by DOE CMSN, ONR, NSF, and ARO. Calculations were performed at the CPD and W\&M SciClone.
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