It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis(para-pyridyl)acetylene(BPPA) tetramer on Au(111) surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular “non-bonded” region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy. It has been said that intermolecular interaction, crucial in a plenty of chemical and physical processes, may vary in the presence of metal surface. However, such modification is yet to be quantitatively revealed. Here, we present a systematical density functional theory study on adsorbed bis (para-pyridyl) acetylene (BPPA) tetramer on Au (111) surface. We were observed unusually high electron density between two head-to-head N atoms, an intermolecular “non- bonded” region, in adsorbed BPPA tetramer. This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA, as squeezed by a newly revealed N-Au-N threecenter bonding.This bond, together with the minor contribution from N .. .HC intermolecular hydrogen bonding, shortens the NN distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV, effectively to a surface-confined in-plane pressure. The overlapped non-bonding vvavefunction hybr idization arising from the effective pressure induced by the N-Au-N three-center bonding, as not been fully recognized in earlier studies, was manifested in non-contact Atomic Force Microscopy.