Correlation energy within exactexchange adiabatic connection fluctuationdissipation theory: Systematic development and simple approximations
Abstract
We have calculated the correlation energy of the homogeneous electron gas (HEG) and the dissociation energy curves of molecules with covalent bonds from an efficient implementation of the adiabatic connection fluctuation dissipation expression including the exactexchange (EXX) kernel. The EXX kernel is defined from firstorder perturbation theory and used in the Dyson equation of timedependent densityfunctional theory. Within this approximation (RPAx), the correlation energies of the HEG are significantly improved with respect to the random phase approximation (RPA) up to densities of the order of r_{s}≈10. However, beyond this value, the RPAx response function exhibits an unphysical divergence and the approximation breaks down. Total energies of molecules at equilibrium are also highly accurate, but we find a similar instability at stretched geometries. Staying within an exact firstorder approximation to the response function, we use an alternative resummation of the higherorder terms. This slight redefinition of RPAx fixes the instability in total energy calculations without compromising the overall accuracy of the approach.
 Publication:

Physical Review B
 Pub Date:
 September 2014
 DOI:
 10.1103/PhysRevB.90.125150
 arXiv:
 arXiv:1409.0354
 Bibcode:
 2014PhRvB..90l5150C
 Keywords:

 71.15.Mb;
 71.10.Ca;
 31.15.E;
 Density functional theory local density approximation gradient and other corrections;
 Electron gas Fermi gas;
 Densityfunctional theory;
 Condensed Matter  Strongly Correlated Electrons;
 Physics  Chemical Physics
 EPrint:
 doi:10.1103/PhysRevB.90.125150