Fig. 4: Convergence performance of ADAPT-GCIM in computing the ground states of four molecules.

For comparison, results from ADAPT-VQE, ADAPT-VQE-GCIM, and ADAPT-VQE-GCIM(1) are also included. The shaded region is when error is smaller than the chemical accuracy. ADAPT-VQE and ADAPT-VQE-GCIM are set to converged when the sum of the magnitudes of all gradients falls below 10−4. ADAPT-GCIM is terminated if the changes on lowest eigenvalue are under 10−6 a.u. for at most 10 (for H4) or 25 (the other molecules) consecutive iterations, where this threshold depends on the size of the operator pool and the amount of unchosen ansätze.