Quantum Monte Carlo determination of the atomization energy and heat of formation of propargyl radical

The quantum Monte Carlo (QMC) method is used to compute the atomization ene rgy and the heat of formation of the propargyl radical, C3H3. The effective core potential and fixed-node approximations are used in the diffusion Mon te Carlo (DMC) variant of QMC. Two generalized gradient approximation densi ty functionals, B3LYP and B3PW91, are also applied for comparison. The atom ization energy determined by these methods is 606.12 kcal/mol (B3LYP), 610. 24 kcal/mol (B3PW91), and 607.6(0.6) (DMC). The latter compares favorably w ith separate measurements of 608.0(3.0) and 608.5(1.2) kcal/mol. The Delta H-f(298) determined by these methods is 84.03 kcal/mol (B3LYP), 79.91 kcal/ mol (B3PW91), 82.5(0.6) (DMC), and two independent measurements yield value s of 82.5(3.0) and 81.5(1.2) kcal/mol. (C) 2000 American Institute of Physi cs. [S0021-9606(00)30231-8].