Molecular Magnets 
Iron core of the molecular magnet Fe8. The spheres represent the iron ions and their arrows illustrate one of several possible ferrimagnetic orderings which can lead to the observed S = 10 molecular ground state.

Several transition metal-containing molecular nanostructures of intermediate nuclearity have been synthesized. These structures contain on the order of 10 metal ions and have novel physical and magnetic properties which are favored by their mesoscopic dimensions. Displaying characteristics which are borderline between those of simple paramagnets and those of bulk magnetic materials, these transition metal-containing molecular nanostructures have attracted considerable interest from physicists, chemists and material scientists.

Athough much experimental and theoretical effort has been devoted to understanding spin dynamics and tunneling rates in molecular magnets, little attention has been given to the first principle calculation of their electronic structures and to the computational prediction of their magnetic properties such as magnetic anisotropies. Our efforts are devoted to understanding the detailed electronic configurations which ultimately give rise to the observed magnetic properties of molecular magnets. Such understanding can significantly contribute to the work of synthetic material scientists who try to engineer molecular magnets for potential technological applications.  

Computational Electronic Structure of DNA

                                                                       

(a) The double-helix structure of DNA consists of two linear strands with four bases ­ guanine (G), cytosine (C), adenine (A) and thymine (T). The A bases on one strand pair up with the complementary T bases on the other strand, while G pairs up with C.

(b) Electron-transfer-rate experiments have been carried out on DNA molecules that have donor and acceptor groups added at each end. In electronic-transport experiments, the DNA molecules are sandwiched between two metal electrodes. [Source: C. Dekker and M. Ratner, physicsweb.org, 2001]

DNA has a crucial role in biological systems as a carrier of genetic information. More recently, however, some  experiments suggest that DNA can also be seen as an efficient  "molecular wire" which offers virtually no resistance to electronic conductivity. We are interested in elucidating, by means of computational methods of electronic structure, the possible pathways for electron transfer which give rise to the conduction properties of DNA.
 

Computational Electronic Structure of Nanotubes

Single-Walled Carbon Nanotube of (3,3) Chirality. 
Single walled nanotubes (SWCNs) are carbon-based nanostructures with  remarkable electronic properties. The small diameter of SWCNs gives their physical properties a  quasi one-dimensional character. That is SWCNs can be regarded as one-dimensional quantum wires. SWCNs are thought to be potentially useful in the design of nanoscale electronicdevices and, due to their mechanical properties, for developing strong polymer-based materials. We are studying the electronic structure of nanotube models to establish some correlations between their geometric structures,  density of states (DOS), and characteristics of their valence and conduction bands.  We are particularly interested in studying possible magnetic properties, such as intrinsic spin polarization, which is believed to occur in some  heterostructured (doped) nanotubes.   Such heterostructures may serve as "spin-polarizers" during electron transport.  

 

Delocalized Electron Density.
The figure shows a delocalized one-electron valence state that we have obtained from density functional theory (DFT) calculations on the (3,3) nanotube shown above. The one-electron density spans the entire nanostructure indicating that the molecular geometry allows, by itself,   intrinsic delocalization  whereby some valence electrons are completely delocalized along the axis of the nanotube.                                            
 

01/15/2004. 

Prof. Jorge Rodríguez Receives Prestigious NSF CAREER Award. The National Science Foundation (NSF) has granted a CAREER award to Jorge Rodríguez,  Assistant Professor of Physics at Purdue. This award intends to foster Prof. Rodriguez's theoretical and computational research  on biomolecular and mesoscopic physics and, in particular, on quantum models of the electronic structure and biological function of  magnetically ordered metalloproteins. This award also intends to contribute to Prof. Rodriguez's various educational efforts.  According to NSF,  the CAREER is its "most prestigious award for new faculty members. The CAREER program recognizes and supports the early career-development activities of those teacher-scholars who are most likely to become the academic leaders of the 21st century." The award carries with it funding for five consecutive years.  

09/14/2002. The antiferromagnetic spin couplings in structural models for diiron-oxo proteins  have been predicted with unprecedented accuracy. First principle calculations based on density functional theory(DFT), in conjunction with high performance supercomputers, were carried out to obtain these results. Our computational method is potentially a powerful and novel alternative to susceptibility or other experimental methods which have been traditionally used to determine magnetic parameters. We have reported these results in an extensive publication [J. Chem. Phys. 116, 6253-6270, 2002].