It is universally acknowledged that the Generalized Liquid Drop Model(GLDM)has two advantages over other a decay theoretical models:introduction of the quasimolecular shape mechanism and proximity energy.In the past few decades,the original proximity energy has been improved by numerous works.In the present work,the different improvements of proximity energy are examined when they are applied to the GLDM for enhancing the calculation accuracy and prediction ability of a decay half-lives for known and unsynthesized superheavy nuclei.The calculations of a half-lives have systematic improvements in reproducing experimental data after choosing a more suitable proximity energy for application to the GLDM.Encouraged by this,the a decay half-lives of even-even superheavy nuclei with Z=112-122 are predicted by the GLDM with a more suitable proximity energy.The pre-dictions are consistent with calculations by the improved Royer formula and the universal decay law.In addition,the features of the predicted a decay half-lives imply that the next double magic nucleus after208Pb is298F1.