## PARSEC at NNIN

## PARSEC

#### Pseudopotential Algorithms for Real Space Energy Calculations

**Overview:**

The PARSEC package provides users with the ability to solve the electronic structure of confined systems such as atomic clusters, molecules, and quantum dots by using a real space approach. The current version can calculate forces and is capable of performing ab-initio molecular dynamics studies, including simulated annealing.

The code takes advantage of three common approximations to perform electronic structure calculations. These include the Born-Oppenheimer approximation (seperation of nuclear and electronic degrees of freedom), pseudopotentials, and local density or generalized gradient approximations for exchange and correlation effects.

PARSEC solves the Kohn-Sham equation on a cubic grid in real space and is ideally suited for situations where approaches that rely on periodic boundary conditions (i.e. plane-waves, LMTO) can fail. The real space approach is particularly important in low dimensional systems such as atomic clusters, molecules, finite nanowires, and quantum dots.

A MATLAB version that can run on a laptop is now available by request from the developers.

**Applications:**

- Electronic structure of Low Dimension Structures (Quantum Dots, Clusters, Molecules)
- Optical Absorption and Spectra
- Charged Systems
- Time Dependent Density Functional Theory - Molecular Dynamics
- Structural Relaxations
- Electronic Transport

**Developers:**

J. R. Chelikowsky, Y. Saad, M. Troullier, A. Stathopoulos, K. Wu, S. Ogut, H. Kim, M. Jain, I. Vasilev, L. Kronik, R. Burdick, A. Makmal, M. Alemany, M. Tiago, C. Pickard, J. Nocedal, J. L. Martins, and K. Burke (for specific contributions see this page)

Much of the work on this program was done at the University of Minnesota with subsequent contributions from the Weizmann Institute and the Institute for Computational Engineering and Sciences (ICES) at the University of Texas.

**Getting Started:**

PARSEC Website (contains source code, documentation, and much more!)

User Guide for Version 1.1

Lectures and Tutorials from the 2006 CNF Fall Workshop "Building Nanostructures Bit by Bit""Real space approaches for modeling clusters, nanowires, and more (pdf)", (Murilo Tiago, University of Texas)

[Video of talk on CNF MediaSite]

Parsec Tutorial by Murilo Tiago (pdf version) (html)

Running PARSEC using NNIN resources

Contact Derek Stewart stewart (at) cnf.cornell.edu or Michael Stopa, stopa (at) deas.harvard.edu

**Relevant Research Articles:**

**The First Article **

- Chelikowsky, J. R., Troullier, N., and Saad, Y., "
*Finite-difference pseudopotential method: Electronic structure without a basis*", Physical Review Letters,**72**, 1240, (1994).

**Overview Papers**

- A. Natan, A. Benjamini, D. Naveh, L. Kronik, M. L. Tiago, S. P. Beckman, and J. R. Chelikowsky "
*Real space pseudopotential method for first principles calculations of general periodic and partially periodic systems*",*Phys. Rev. B*,**78**, 075109 (2008). - L. Kronik, A. Makmal, M. L. Tiago, M. M. G. Alemany, M. Jain, X.-Y. Huang, Y. Saad, and J. R. Chelikowsky, "
*PARSEC - the pseudopotential algorithm for real-space electronic structure calculations: recent advances and novel applications to nano-structures*",*Phys. Stat. Sol. (b)*,**243**, 1063 (2006).

**Recent Applications and Developments...**

- Kong, L. Z., Tiago, M. L., and Chelikowsky, J. R., "
*Real-space pseudopotential method for electron transport properties of nanoscale junctions"*, Physical Review B,**73**, 195118 (2006). - Huang, X., Makmal, A., Chelikowsky, J. R., and Kronik, L., "
*Size-dependent Spintronic Properties of Dilute Magnetic Semiconductor Nanocrystals*", Physical Review Letters,**94**, 236801, (2005). - Li, S., Alemany, M. G., and Chelikowsky, J. R.,"
*Ab-initio calculations of the photoelectron spectra of transition metal clusters*", Physical Review B,**71**, 165433, (2005). - Kuemmel, S., Kronik, L., and Perdew, J. P.,"
*Electrical response of molecular chains from density functional theory*", Physical Review Letters,**93**, 213002, (2004). - Chelikowsky, J. R., Kronik, L., and Vasiliev, I., "
*Time dependent density functional calculations for the optical spectra of molecules, clusters, and nanocrystals*", Journal of Physics: Condensed Matter,**15**, R1517 (2003). - Vasiliev, I., Ogut, S., and Chelikowsky, J. R., "
*Ab Initio Optical Absorption and Electronic Excitations in Hydrogenated Silicon Quantum Dots*", Physical Review Letters,**89**1813, (2001).*,* - Vasiliev, I., Ogut, S., and Chelikowsky, J. R., "
*First Principles Density Functional Calculations for Optical Spectra of Clusters and Nanocrystals*", Physical Review B,**65**, 115416, (2002). - Burdick, W. R., Saad, Y., Kronik, L, Jain, M., Vasiliev, I., and Chelikowsky, J. R., "
*Parallel Implementation of Time-Dependent Density Functional Theory*", Computer Physics Communications,**156**, 22, (2003). - Melnikov, D. V., and Chelikowsky, J. R., "
*Quantum confinement in phosphorus-doped silicon nanocrystals*", Physical Review Letters,**92**, 046802, (2004).

### Questions, Comments...

Please contact:

Derek Stewart

stewart (at) cnf.cornell.edu

Cornell Nanoscale Science and Technology Facility, Cornell University