Numerical simulation of quantum anharmonic oscillator, embedded within an infinite square well potential, by matrix methods using Gnumeric spreadsheet

The quantum anharmonic oscillator has been solved numerically using matrix diagonalization technique. The interaction potential consisting of quadratic (1/2kx(2)) and quartic (lambda x(4)) terms is embedded within an infinite square well potential of appropriate width, 'a' and its sine eigen functions are used as basis functions 'N' for the employed matrix method. The energy eigen values for the resultant Hamiltonian are solved in a free open source software (FOSS), Gnumeric, a simple worksheet environment. The numerical parameters 'a' and 'N' are optimized to converge to the expected energies for harmonic oscillator and those for anharmonic oscillator from perturbation theory for small values of physical parameter, 'lambda'. The pure quartic oscillator is studied for both small and large values of lambda and validated with results obtained from other numerical techniques. The breakdown of perturbation approximation for large values of lambda is also shown.