Second-Order Correction to Feynman's Path-Integral Calculation of the Polaron Self-Energy
John T. Marshall, Laney R. Mills · Physical review. B, Solid state · 1970
The second-order term of a series expansion for the exact Feynman path-integral expression for the polaron self-energy is calculated. For all values of the polaron coupling constant, the result yields a correction of less than 2% to Feynman's variational approximation of the polaron self-energy.