Capturing spin fluctuations in CaCuO2: Ab initio quantum Monte Carlo calculations with multideterminant wave functions

We present an advanced ab initio quantum Monte Carlo (QMC) calculation of the ground state of undoped CaCuO2. We extend the traditional single-determinant Slater-Jastrow approach to include multideterminant wave functions, inhomogeneous Jastrow factors, and orbital optimization. Our results demonstrate not only an improvement in the variational bound of the ground state energy - 2.3 eV per formula unit lower than previous state-of-the-art techniques - but also confirm the presence of spin fluctuations in multideterminant wave functions in a strongly correlated cuprate system, which is integral to understanding high-Tc superconductivity. This is a demonstration of capturing spin fluctuations in QMC wave functions on a cuprate, establishing the groundwork for studies on doped cuprates in the superconducting state, where spin fluctuations require more accurate characterization.