DOE Physicists at Work Archive

**DOE Physicists at Work**

**Profiles of representative DOE-sponsored physicists
doing research at universities and national laboratories**

**Compiled by the Office of Scientific and Technical Information**

**Dr. Lin-Wang Wang**

*Dr. Lin-Wang Wang has a love for theory, extending back to when he was a middle school student in China. * At that time, his parents subscribed for him a popular science magazine. "I was intrigued by the science fictions in that magazine, always couldn't wait for the next issue to come," says Dr. Wang, staff scientist with the Lawrence Berkeley National Laboratory Scientific Computing Group (SCG) of the High Performance Computing Department. One day, while perusing this magazine, he found an interesting article introducing Einstein's theory of special relativity. "After reading it three times, I was still very confused," says Dr. Wang. "Nevertheless, it left me with a deep impression about the amazing world of physics. Until these days, I still remember the picture of a whale swimming in the sea. When the whale swims faster, it is supposed to get shorter."

In high school, with intrigue growing for the mysteries of theoretical physics, Lin-Wang had what he thought was a great idea. "After learning that heat is just a form of energy, I thought, why not build a car which converts the heat into energy, perhaps leaves a cold road behind?" Unfortunately, he quickly learned that there is a second law of thermodynamics which cast a shadow on his plans. "Too great an idea to give up, I thought about many possible ways and devices to refute this law," says Dr. Wang. "But by the end of my first year in college, I was finally convinced that the second law of thermodynamics is probably right."

As his understanding of physics grew, his interests shifted, and he began to wonder about the measurement problem of quantum mechanics. "What does it mean, this 'measuring a particle, and then the result breaks down to different possibilities,'" he asks. "The process of measurement should be described in the same way as all the other processes, all the way to the experimenter's brain. There should be no breaking down." He eventually found a way to solve this problem in his first graduate year at Cornell University. "But then I found that someone had that idea a long time ago - it is called 'many world interpretation' of quantum mechanics."

These experiences only deepened his interest in the seemingly boundless scope of the world of physics, and for a while, he wasn't sure which field to pursue. Should it be neural network and how the brain works, or the exotic super string theory, or perhaps the chaotic theory in nonlinear dynamics? He had written a program trying to simulate how a monkey thinks, and he had taken most of the high energy physics courses. But finally he settled down with condensed matter physics. "It is more practical and relevant to our everyday like," says Dr. Wang. But he leans toward the theoretical side, rather than the experimental. "I do not think I am a handy man for experiment; the only experiments I like to do are the "thought experiments." In particular, he likes to think while walking. "Once, after strolling around a quiet parking lot for too long while thinking about a problem, I was followed by a police car suspecting something heinous from me!"

Dr. Wang's current research is focused on large scale electronic structure calculations of nanosystems using supercomputers. His first encounter with a computer included paper tapes and punching holes on the tapes while he was an undergraduate student in Shanghai JiaoTong University in mainland China. The more serious encounter with computers came when he attended graduate school at Cornell University in 1985, through the China-U.S. Physics Examination and Application (CUSPEA) program. "It was an IBM mainframe, and you walked to the computer room to use it. Now that the power of the computer has increased thousands of folds, it has become a powerful tool to investigate many physics problems, especially for complicated systems like nanostructures, where the traditional analytical tools are often not applicable."

One of Dr. Wang's passions is to invent new computational algorithms related to material science simulations and electronic structure calculations. He has invented quite a few of them, from thousand-atom quantum dot calculations to new ways to calculate electronic transports. "Before, people can only calculate a few hundred atoms," says Dr. Wang. "But now, from a few thousand up to a million atom nanosystems can be calculated in a first principle accuracy." The goal is to improve the status of material science simulation, making it similar to engineering, where a building or an airplane can be designed inside a computer with all the physics involved well understood. "We are far from there yet, but we are getting closer, thanks to the continuous improvement of computer power and the development of new algorithms."

Dr. Wang's research is sponsored by the Department of Energy. After receiving his PhD in physics in 1991 from Cornell University, he completed a post doctoral position at the National Renewable Energy Laboratory (NREL) in Denver Colorado, under the supervision of Dr. Alex Zunger. Dr. Wang then worked as a research scientist in Material Simulation Inc. in San Diego in 1995, before returning to NREL as a staff scientist. In 1999, he joined the Lawrence Berkeley National Lab. He has been an active user of the supercomputers in National Energy Research Scientific Computing Center since 1993.

**Dr.** **Lin-Wang Wang****'s articles accessed via OSTI:**

Thick-Restart Lanczos Method for Electronic Structure Calculations

Defects in Photovoltaic Materials and the Origins of Failure to Dope Them: Preprint

Coherent phase stability in Al-Zn and Al-Cu fcc alloys: The role of the instability of fcc Zn

Real and spurious solutions of the 8x8 k∙p model for nanostructures

Parallel Empirical Pseudopotential Electronic Structure Calculations for Million Atom Systems

Large-scale local-density-approximation band gap corrected GaAsN calculations

Calculating the influence of external changes on the photoluminescence of a CdS quantum dot

Calculations of carrier localization in In

_{x}Ga_{1-x}N

Linearly polarized emission from colloidal semiconductor quantum rods

Dependence of the band structure on the order parameter for partially ordered Ga

_{x}In_{1-x}P alloys

Thomas-Fermi charge mixing for obtaining self-consistency in density functional calculations

Calculation of thermodynamic, electronic, and optical properties of monoclinic Mg

_{2}NiH_{4}

Generating charge densities of fullerenes

Charge-density patching method for unconventional semiconductor binary systems

High energy excitations in CdSe quantum rods

Energy levels of isoelectronic impurities by large scale LDA calculations

First principle calculations of ZnS:Te energy levels

Pseudopotential theory of Auger processes in CdSe quantum dots

Quantization condition of quantum-well states in Cu/Co(001)