Exchange-correlation energy from pairing matrix fluctuation and the particle-particle random phase approximation

摘要: Despite their unmatched success for many applications, commonly used local, semi-local, and hybrid density functionals still face challenges when it comes to describing long-range interactions, static correlation, electron delocalization. Density of both the occupied virtual orbitals are able address these problems. The particle-hole (ph-) Random Phase Approximation (RPA), a functional orbitals, has recently known revival within theory community. Following up on an idea introduced in our recent communication [H. van Aggelen, Y. Yang, W. Phys. Rev. A 88, 030501 (2013)], we formulate more general adiabatic connections correlation energy terms pairing matrix fluctuations described by particle-particle (pp-) propagator. With numerical examples pp-RPA, lowest-order approximation pp-propagator, illustrate potential approximations based fluctuations. pp-RPA is size-extensive, self-interaction free, fully anti-symmetric, describes strong limit H2, eliminates delocalization errors H2(+) other single-bond systems. It gives surprisingly good non-bonded interaction energies--competitive with ph-RPA--with correct R(-6) asymptotic decay as function separation R, which argue mainly attributable its second-order term. While tends underestimate absolute energies, relative energies: much better atomization energies than ph-RPA, no tendency underbind, reaction similar quality. connection fluctuation paves way promising new approximations.