Conformer equilibrium from RealQM ΔE

For molecules with two competing conformers (e.g.\ ethanol gauche vs anti, butane gauche vs anti, peptide ϕ/ψ rotamers): compute the energy difference ΔE = E(B) − E(A) by running RealQM at the two geometries, then form the canonical equilibrium ratio:

K(T) = [B] / [A] = g_B/g_A · exp(−ΔE / k_B T)

g_A and g_B are degeneracies (e.g.\ g_gauche=2, g_anti=1 for two equivalent gauche minima).

Inputs

Conformer A (lower energy):
label , degeneracy g_A , E_A Ha

Conformer B (higher):
label , degeneracy g_B , E_B Ha

Default ΔE = 0.0008 Ha ≈ 2.1 kJ/mol — typical small-organic conformer gap.
Ethanol experimental (anti, gauche): ΔE ≈ 0.0006 Ha = 0.4 kcal/mol; gauche has g=2.

Equilibrium ratio K(T) = [B]/[A]

T (K)	k_B T (Ha)	K = [B]/[A]	P(A) %	P(B) %