Title: A microscopic theory of photonucleation: Density functional approach to the properties of a fluid of two-level atoms, a part of which is excited
Author(s):

	O.Derzhko (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine) ,
	V.Myhal (The Ivan Franko National University of L'viv, Department for Theoretical Physics, 12 Drahomanov Street, 79005 L'viv, Ukraine)

We use the density functional method to examine the properties of the nonuniform (two-phase) fluid of two-level atoms, a part of which is excited. From the analysis of the equation of state of a gas of two-level atoms, a part of which is excited, the following density functional of the grand thermodynamical potential emerges

Ω[ρ(r)] =Ω_CS[ρ(r)] -6σ³a(c₁,T)π^-1 ∫_{|r1-r2|≥ 2σ}dr₁dr₂ ρ(r₁)ρ(r₂)|r₁-{\bf{r}}_2|^-6

with

a(c₁,T) =32^-1a²v(E₁-E₀) (c₀-c₁+2c₀c₁E₁-E₀[kT]^-1)

(here Ω_CS[ρ(r)] is the Carnahan-Starling term, σ is the atom radius, v=4/3πσ³, c₁ is the concentration of excited atoms, c₀+c₁=1, E₁-E₀ is the excitation energy and a is the dimensionless parameter which characterizes the atom). We use this expression to calculate the nucleation barrier for vapor-to-liquid phase transition in the presence of excited atoms.

Key words: photonucleation, nucleation barrier, density functional approach
PACS: 64.70.Fx, 82.65.Dp, 62.60.Nh, 64.60.Qb