Adiabatic-Connection Fluctuation-Dissipation Density-Functional Theory Based on Range Separation

An adiabatic-connection fluctuation-dissipation theorem approach based on a range separation of electron-electron interactions is proposed. It involves a rigorous combination of short-range density-functional and long-range random phase approximations. This method corrects several shortcomings of the standard random phase approximation and it is particularly well suited for describing weakly bound van der Waals systems, as demonstrated on the challenging cases of the dimers ${\mathrm{Be}}_2$ and ${\mathrm{Ne}}_2$.

Figure 1

RPA, RPAx, and $\mathrm{RSH}+\mathrm{RPAx}$ total energies of ${\mathrm{Ne}}_2$ at equilibrium distance (5.84 Bohr) with respect to the basis size.

Figure 2

Interaction energy curves of ${\mathrm{Be}}_2$ and ${\mathrm{Ne}}_2$ calculated in RPA, MP2, RPAx, and $\mathrm{RSH}+\mathrm{RPAx}$. The basis is cc-pV5Z for ${\mathrm{Be}}_2$ and aug-cc-pV5Z for ${\mathrm{Ne}}_2$. The accurate curves are from Refs. 37, 38.