Three dimensional elongation method for large molecular calculations

► The CPU time to form Fock matrix of 3D-elongation method is accelerated if elongation cutoff technology is triggered. ► The CPU time to solve Fock matrix of 3D-elongation method is faster than conventional one if there is (are) unit(s) in frozen region. ► The fewer SCF iterations of 3D-elongation calculations in a given step are attributed to the better initial guess. ► The average deviation of total energy by 3D-elongation method is 4.7 × 10−7 au/atom for model system calculations.