▁constant ▁C v ▁and ▁dynam ical ▁image ▁plane ▁Z 0 ▁of ▁rare ▁gas ▁atoms ▁on ▁various ▁metal ▁surfaces . ▁ ▁The ▁increasing ▁of ▁C v ▁from ▁He ▁to ▁X e ▁for ▁all ▁metal ▁substr ates ▁is ▁caused ▁by ▁the ▁larger ▁atomic ▁polar iz ability ▁of ▁the ▁heav ier ▁rare ▁gas ▁atoms . ▁ ▁For ▁the ▁position ▁of ▁the ▁dynam ical ▁image ▁plane , ▁it ▁decre ases ▁with ▁increasing ▁die lect ric ▁function ▁and ▁is ▁typically ▁on ▁the ▁order ▁of ▁ 0 . 2   Å . ▁ ▁Ph ysis or ption ▁potential ▁ ▁Even ▁though ▁the ▁van ▁der ▁Wa als ▁interaction ▁is ▁attract ive , ▁as ▁the ▁ad s or bed ▁atom ▁moves ▁closer ▁to ▁the ▁surface ▁the ▁wave function ▁of ▁electron ▁starts ▁to ▁overlap ▁with ▁that ▁of ▁the ▁surface ▁atoms . ▁ ▁Further ▁the ▁energy ▁of ▁the ▁system ▁will ▁increase ▁due ▁to ▁the ▁orth og on ality ▁of ▁wave functions ▁of ▁the ▁approaching ▁atom ▁and ▁surface ▁atoms . ▁ ▁This ▁Paul i ▁ex clusion ▁and ▁rep ulsion ▁are ▁particularly ▁strong ▁for ▁atoms ▁with ▁closed ▁val ence ▁shell s ▁that ▁domin ate ▁the ▁surface ▁interaction . ▁ ▁As ▁a ▁result , ▁the ▁minimum ▁energy ▁of ▁phys is or ption ▁must ▁be ▁found ▁by ▁the ▁balance ▁between ▁the ▁long - range ▁van ▁der ▁Wa als ▁att raction ▁and ▁short - range ▁Paul i ▁rep ulsion . ▁ ▁For ▁instance , ▁by ▁separ ating ▁the ▁total ▁interaction ▁of ▁phys is or ption ▁into ▁two ▁contributions — a ▁short - range ▁term ▁dep icted ▁by ▁Hart