An Effective Nuclear Charge Database Based on Slater's Rules: Implementation and Validation (v1.0)

This technical whitepaper describes a modern database and REST API for querying atomic effective nuclear charge (Z_eff) for main-group elements (H–Kr). The core calculation strictly follows J. C. Slater's shielding constant rules (1930), without modification. Validation against Clementi and Raimondi's SCF-derived benchmark values (1963) demonstrates consistent agreement, with deviations within 2.1% for second-period elements and zero deviation for third- and fourth-period s-block elements. The free tier provides 1,000 queries per month for academic research. A Chinese version is available as a supplementary file.