With the natural splitting of a Hamiltonian system into kinetic energy and potential energy, we construct two new optimal thirdorder force-gradient symplectic algorithms in each of which the norm of fourth-order truncation errors is minimized. They are both not explicitly superior to their no-optimal counterparts in the numerical stability and the topology structure-preserving, but they are in the accuracy of energy on classical problems and in one of the energy eigenvalues for one-dimensional time-independent Schrödinger equations. In particular, they are much better than the optimal third-order non-gradient symplectic method. They also have an advantage over the fourth-order non-gradient symplectic integrator. symplectic integrators, symplectic scheme-shooting method, celestial mechanics, time-independent Schrödinger equation, energy eigenvalues, numerical stability, bisection method, topological structure PACS: 02.70.-c, 03.65.-w, 95.10.Ce