This expansion is only applicable if the largest absolute value of the eigenvalues of A n is less than one, λ max = max (|λ i |) < 1, and it converges poorly as the magnitude of the eigenvalue approaches one. As the authors of LINCS note, angle-constrained butane has λ max = 0.8, while angle-constrained pentane has λ max = 1.2. The reason for coupled constraints being prone to fail is that increasing powers (p) of the A n matrix represent the coupling effect of constraints that are p constraints away. The largest power p in the truncated series eq 3 corresponds to the requested LINCS order (lincs order). In coupled triangles, the 3 rd constraint away from a given constraint is already the constraint itself. As such, for highly coupled geometries the expansion in eq 3 usually converges slowly or not at all. Consequently, the Gromacs MD simulation engine internally doubles the requested lincs order for all constraints involved in triangular arrangements. As the A n matrix can be diagonalized, one can conveniently assess the convergence of eq 3 with increasing lincs order based on how fast λ p max decreases. Under typical bond distortions, λ max is approximately 0.4. Combined with lincs order = 4, the error of the expansion is proportional to (λ max ) lincs order = 0.4 . Here, we use this relationship as a rule-of-thumb to estimate the lincs order required for convergence.