CCSD(T)/Def2-TZVPP , no solvent 

HCCH                         HCC• + H•                        CC + H•

 -77.1891247  =   (-76.4690787  +  -0.4998098)  = (-75.7846187  +  -0.4998098)

-77.1891247  = -76.9688885,  -76.4690787  =  -76.2844285
      
ΔE  138.2                   ΔE     115.9  
      
ΔΔE = 22.3 kcal/mol