We model the adsorption and STM imaging of benzene on Si͑100͒ by using first principles density functional methods and a perturbation approach for the tunneling current. The simulations are well in accordance with experimental data and reproduce the adsorption energies and the energy differences between adsorption sites remarkably well. We were able to simulate images and line scans of the two principal adsorption geometries and to show that they reproduce the actual measurements. The chemical

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... ature of the tip in measurements is discussed and it is shown that a tip structure protruding several layers from the crystal face and terminated by a tungsten atom gives the best agreement with measurements. The results confirm the view that tunneling is dominated by a single tip atom.