Toward Chemical Accuracy Using the Jastrow Correlated Antisymmetrized Geminal Power .

Herein, we report accurate atomization energy calculations for 55 molecules in the Gaussian-2 (G2) set using lattice regularized diffusion Monte Carlo (LRDMC). We compare the Jastrow-Slater determinant with a more flexible JsAGPs (Jastrow correlated antisymmetrized geminal power with singlet correlation) . AGPs is built from pairing functions, which explicitly include pairwise correlations among electrons, and hence, this is expected to be more efficient in recovering the correlation energy. The AGPs wave functions are first optimized at the variational Monte Carlo (VMC) level, which includes both the Jastrow factor and the nodal surface optimization. This is followed by the LRDMC projection of the . Remarkably, for many molecules, the LRDMC atomization energies obtained using the JsAGPs reach chemical accuracy (∼1 kcal/mol), and for most other molecules, the atomization energies are accurate within ∼5 kcal/mol. We obtained a mean absolute deviation of 1.6 kcal/mol with JsAGPs and 3.2 kcal/mol with JDFT (astrow factor + Slater determinant with orbitals) . This work shows the effectiveness of the flexible AGPs for atomization energy calculations and electronic structure simulations in general.