**Cosmological Constant (Λ):** Represents the energy density of empty space. Units: m⁻².

**Reduced Planck Constant (ħ):** A fundamental constant in quantum mechanics. Units: J·s.

**Speed of Light (c):** The speed of light in a vacuum. Units: m/s.

**Hubble Constant (H₀):** The rate of expansion of the universe. Units: km/s/Mpc.

**Dark Energy Density Parameter (Ω_Λ):** The proportion of the universe's energy density that is attributed to dark energy.

**Output Unit:** Choose the unit for the vacuum energy density output.