If the anharmonicity of the harmonic boost potential ∆V (r) is small, then ∆V (r) follows a near Gaussian distribution and the cumulant expansion to the second order can be used to approximate the exponential average term e β∆V (r) , where β denotes the thermodynamic beta or 1/k B T . This exponential average term e β∆V (r) is needed to reweight and recover the original free energy landscape from GaMD. Readers can refer to the original GaMD paper for specific details about energetic reweighting with cumulant expansion to the second order.