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Next: 17.2.5 Rangehybrid methods (RANGEHYBRID) Up: 17.2 Directives Previous: 17.2.3 Exact exchange computation   Contents   Index   PDF

17.2.4 Double-hybrid functionals (DH, DSDH)

DH, ax, ac

initiates a double-hybrid calculation (Ref. [1]) where $a_x$ is the fraction of HF exchange and $a_c$ is the fraction of MP2 correlation. A self-consistent KS calculation is performed with functional $a_x E_x^{\text{HF}} + (1-a_x) E_x^{\text{DFT}}[\rho] + (1-a_c) E_c^{\text{DFT}}[\rho]$. One then needs to call the MP2 program to add the MP2 contribution $a_c E_c^{\text{MP2}}$. If $a_c$ is not given, $a_c=a_x^2$ is assumed, according to Ref. [2].

DSDH, ax, ac

initiates a density-scaled double-hybrid calculation (Ref. [2]) where $a_x$ is the fraction of HF exchange and $a_c$ is the fraction of MP2 correlation. A self-consistent KS calculation is performed with functional $a_x E_x^{\text{HF}} + (1-a_x) E_x^{\text{DFT}}[\rho] + E_c^{\text{DFT}}[\rho] - a_c E_c^{\text{DFT}}[\rho_{1/\sqrt{a_c}}]$, where $\rho_{1/\sqrt{a_c}}$ is the scaled density. In the case of meta-GGA functionals, the kinetic energy density $\tau$ is also scaled, according to Ref. [3]. One then needs to call the MP2 program to add the MP2 contribution $a_c E_c^{\text{MP2}}$. If $a_c$ is not given, $a_c=a_x^2$ is assumed, according to Ref. [2].

Example of input for B2-PLYP calculation (Ref. [1]):
{ks,b,lyp;dh,0.53,0.27;}
mp2;

Example of input for 1DH-BLYP calculation (Ref. [2]):
{ks,b,lyp;dh,0.65;}
mp2;

Example of input for DS1DH-TPSS calculation (Ref. [3]):
{ks,tpss;dsdh,0.725;}
mp2;

Unrestricted calculations (uks, ump2) can also be done.

References:
$[1]$ S. Grimme, J. Chem. Phys. 124, 034108 (2006).
$[2]$ K. Sharkas, J. Toulouse, A. Savin, J. Chem. Phys. 134, 064113 (2011).
$[3]$ S. M. O. Souvi, K. Sharkas, J. Toulouse, J. Chem. Phys. 140, 084107 (2014).



Next: 17.2.5 Rangehybrid methods (RANGEHYBRID) Up: 17.2 Directives Previous: 17.2.3 Exact exchange computation   Contents   Index   PDF

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