The RDM2(molecule) command computes the spin-free 2-electron reduced density matrix (2-RDM).

The output is a 4-index Array with dimensions  r x r x r x r, where r is the number of the orbitals.

The element A[i,k,j,l] of the output Array correponds to the element of the 2-RDM D2[i,j,k,l].

The default method is the 'MP2' method.

The result depends upon the chosen molecule, method, and basis set among other options such as charge, spin, and symmetry.

Because the methods employ Maple cache tables, the procedure only computes the 2-RDM if it has not been previously computed by calling the method directly or indirectly through another property.

$\mathrm{with}\left(\mathrm{QuantumChemistry}\right)\:$

$\mathrm{molecule} ≔ \left[ \left[''H''\, 0\, 0\, 0\right]\, \left[''F''\, 0\, 0\, 0.95\right] \right]\;$

$\mathrm{molecule}≔\left[\left[''H''\,0\,0\,0\right]\,\left[''F''\,0\,0\,0.95000000\right]\right]$

$\mathrm{d2} ≔ \mathrm{RDM2}\left(\mathrm{molecule}\, \mathrm{method}\=\mathrm{Parametric2RDM}\,\mathrm{basis}\=''dz''\right)\;$

$\mathrm{d2}\left[1\,1\,1\,1\right]\;$

$1.99978160$