On the role of the nonlocal Hartree-Fock exchange in ab initio quantum transport: H2 in Pt nanocontacts revisited

We propose a practical way to overcome the ubiquitous problem of the overestimation of the zero-bias and zero-temperature conductance, which is associated with the use of local approximations to the exchange-correlation functional in density-functional theory when applied to quantum transport. This is done through partial substitution of the local exchange term in the functional by the nonlocal Hartree-Fock exchange. As a nontrivial example of this effect we revisit the smallest molecular bridge studied so far: a H(2) molecule placed in between Pt nanocontacts. When applied to this system the value of the conductance diminishes as compared to the local-exchange-only value, which is in close agreement with the results predicted from time-dependent current-density-functional theory. Our results issue a warning message on recent claims of perfect transparency of a H(2) molecule in Pt nanocontacts.