CCM Research Applications Algorithms & Modeling Semiconductors Magnetic materials Oxides and dielectric materials Nanostructures Algorithms & Modeling Apply “practical” quantum mechanics methods for modeling materials Solve large eigenvalue problems using subspace filtering Funding: DOE, NSF, Welch Foundation Affiliated Faculty Alex Demkov Juan Sanchez Research Staff: Jaime Souto-Casares, Yuki Sakai, Masahiro Sakuai Jim Chelikowsky Director Brief description of some of the research activities in PADAS: Fast algorithms for robust (i.e., automatic, black box) analysis for medical images. Typically, problem-specific algorithms Top left image: MRI FLAIR Image of patient with Grade IV glioma. Top right image: Estimated segmentatio to Grey matter, white matter, cerebrospinal fluid, and tumor Bottom image: Spatial frequency of adult glioblastoma with 3D surface rendering (top) and 2D multiplanar slices (bottom). These tumors tend to appear much more frequently in some brain regions, and this depends on age. The Statistical atlas was constructed with registration algorithms. Simulated atomic force microscopy image of the hexabenzocoronene molecule.

Simulation of Non-Contact Atomic Force Microscopy - CCM The Atomic Force Microscope (AFM) was developed to overcome a basic drawback with scanning tunneling microscopy (STM) - that it can only image conducting or semiconducting surfaces. The AFM, has the advantage of imaging almost any type of surface, including polymers, ceramics, composites, glass, and biological samples. Owing to the complexity of this set up, few theoretical simulations using quantum methods exist. “Non-contact” AFM moves the probe over the molecule or specimen without touching it. This operating mode of AFM is capable of resolving subatomic features for organic molecules.

Simulation of Non-Contact Atomic Force Microscopy - CCM Theoretical Challenge: Determine the forces of the sample on the tip of the probe. Simulated AFM image from first-principles Simulated AFM image using our method Experiment Quantum mechanical methods are used to find the force of the sample on the tip.  This force perturbs the vibrational frequency of the vibrating probe. Calculating accurate values of this force allows us to simulate the AFM image.  Our methods are computationally efficient, and can be used to rapidly screen structural models. We want to avoid methods that require a detailed knowledge of the atomic structure of the probe tip; yet, yield accurate images. Current work includes imaging nanostructures, and large biological molecules.  The atomic structure of silver deposited on a silicon surface.

Simulation of Non-Contact Atomic Force Microscopy - CCM Hexabenzocoronene Molecule Simulated Image Gross, et al. Science, 2012 A properly functionalized nc-AFM tip experiment has been able to resolve differences in the chemical bond in complex organic molecules. These features are properly resolved in our simulations.