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The effect of inhomogenities on single molecule imaging by hard XFEL pulses

We study the local distortion of the atomic structure in small biological samples illuminated by x-ray free electron laser (XFEL) pulses. We concentrate on the effect of inhomogenities: heavy atoms in a light matrix and non-homogeneous spatial distribution of atoms. In biological systems we find both. Using molecular-dynamics type modeling it is shown that the local distortions about heavy atoms are larger than the average distortion in the light matrix. Further it is also shown that the large spatial density fluctuations also significantly alter the time evolution of atomic displacements as compared to samples with uniform density. This fact has serious consequences on single particle imaging. This is discussed and the possibility of a correction is envisaged.