"The new Resonating Valence Bond method for ab-initio electronic simulations"
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The Resonating Valence Bond theory of the chemical bond was introduced soon
after the discovery of quantum mechanics and has contributed to explain the role
of electron correlation within a particularly simple and intuitive approach,
where the chemical bond between two nearby atoms is described by one or more
singlet electron pairs.
We revisit the Pauling's resonating valence bond theory of the chemical bond
within a new formulation,  introduced
by P.W. Anderson soon after the discovery  of High Tc superconductivity.
It is shown that this intuitive picture
of electron correlation becomes now practical and efficient,
and allows us to perform realistic simulations with correlated wavefunctions
corresponding to several hundred atoms.
Few examples will be given: i) in the Beryllium dimer  we
show the accuracy of the method for a particularly difficult case
where single determinant approaches (DFT or Hartree-Fock) miserably fail, ii)
recent finite temperature realistic simulations of liquid hydrogen  and liquid
water.