Release Node Calculation of Unpolarized Atomic Fermi Gas

Using release node techniques in diffusion Monte Carlo method, we study the unpolarized atomic fermi gas in the unitarity regime. We use several types of the trial and guiding wave functions to elucidate the size of fixed-node error. We also analyze the changes in the nodal surfaces for trial functions with varying degree of the pairing strength. We study the bosonic component in guiding functions in order to optimize the extraction of the fixed-node bias and corresponding error bars. The most accurate results for the fixed-node bias were obtained using the the BCS-based guiding functions.