Strain modulation in small molecule physisorption in two dimensions: LEED structure analysis and DFT modeling of the...

The structure of the system was investigated experimentally by means of quantitative LEED I(V) analysis and computationally using dispersion corrected density functional theory (DFT-D). Three different structure models with four, five, and six molecules were considered. The lowest reliability factors and thus best agreement of measured and calculated I(V) curves was found for the structure model containing five molecules per surface unit cell. Essential features of the experimental best-fit adlayer structure are supported by DFT. A slight inclination and lateral shift of twofold coordinated molecules away from the on-top position over Na⁺ adsorption sites is interpreted as compensation of strain between substrate and adlayer.