| How do charge and density fluctuations compete in ionic fluids near gas-liquid criticality when quantum mechanical effects play a role? To gain some insight, long-range Phi(+/-+/-)(L)/r(d+sigma) interactions (with sigma > 0), which encompass van der Waals forces (when sigma = d = 3), have been incorporated in exactly soluble, d-dimensional 1: 1 ionic spherical models with charges +/-q(0) and hard-core repulsions. In accord with previous work, when d > min {sigma, 2} (and q(0) is not too large), the Coulomb interactions do not alter the (q(0) = 0) critical universality class that is characterized by density correlations at criticality decaying as 1/r(d-2+eta) with eta = max{0, 2-sigma}. But screening is now algebraic, the charge-charge correlations decaying, in general, only as 1/r(d+sigma+4); thus sigma = 3 faithfully mimics known noncritical d = 3 quantal effects. But in the absence of full (+, -) ion symmetry, density and charge fluctuations mix via a transparent mechanism: then the screening at criticality is weaker by a factor r(4-2eta). Furthermore, the otherwise valid Stillinger-Lovett sum rule fails at criticality whenever eta = 0 (as, e.g., when sigma > 2) although it remains valid if eta > 0 (as for sigma < 2 or in real d less than or equal to 3 Ising-type systems). |
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