The CD4051 is rarely built-in by default (unlike the NE555 or 2N2222). You have to manually import it.
: While onsemi provides modern "Physical and Scalable" SPICE models for newer components, older parts like the CD4051 may be found within their legacy application notes or ZIP archives under "Technical Documentation" on the specific product landing page. cd4051 spice model link
: Sites like DatasheetArchive aggregate various older models, though these should be tested against the physical CD4051 datasheet to ensure the RONcap R sub cap O cap N end-sub (On-Resistance) matches your specific voltage range. How to Use a CD4051 Subcircuit in LTspice The CD4051 is rarely built-in by default (unlike
: In LTspice, press S to add a SPICE directive and type: .include CD4000.lib (replacing with your actual filename). cd4051 spice model link