Fig. 6: ADAPT-VQE and VQE-UCCSD convergence of the energy with respect to the number of parameters, the total number of derivatives and the circuit depth for O2, CO and CO2 molecules.
From: Variational quantum eigensolver techniques for simulating carbon monoxide oxidation
Fermionic ADAPT-VQE results are marked as "UCCSD-N'', where N indicates the size of the fermionic pool with single and double excitations. Qubit ADAPT-VQE results are referred to as Greedy-N (qubit linear complete pool) and Greedy sd-N (qubit polynomial complete pool with Pauli strings originated from each single and double fermionic excitation), where N is the qubit pool size. "f-UCCSD" refers to VQE-UCCSD result. By the green color we highlight the area, where the chemical accuracy threshold is satisfies. a Energy convergence for O2 molecule at the equilibrium geometry. As far as single qubit operator, which is obtained from each fermionic excitations do not form a complete pool, we add two extra operators to ensure pool completeness. Thus greedy sd pool contains 26 operators in this case. b Energy convergence for CO molecule at the equilibrium geometry. c Energy convergence for CO2 molecule at the equilibrium geometry.
