Making molecules dance to our tune

Dermot Martin takes a look at the interconnected dance of quantum chemistry and super computers

The brilliant French chemist Joseph Louis Gay-Lussac once said of chemistry that one day soon the bulk of all chemical phenomena would be predictable by mathematical insight.

Gay-Lussac died in 1850, hero of the law which states that the volume of any gas increases with temperature if it’s mass and pressure remain constant, but his foresight about the evolution of our knowledge of chemistry at a time when computers had yet to be invented was a measure of his true genius.

Today we can say we have arrived at that destination - with the capability of pulling many of the strings which allow us to make molecules and atoms dance to our tune. But ask the man in the street what is the greatest human advance of the last 75 years and it is odds-on he would say space exploration, or the mapping of the human genome, the development of super computers or even the Internet. He would be unlikely to cite how we are on the brink of conquering the world of atomic and molecular structure.

People are not aware of this ability to shape and steer the very particles of which we ourselves are made in part because it has been achieved in parallel with the evolution of computer technology.

Without our powerful computers, quantum chemistry could not move forward, but without quantum chemistry we would not be able to create the next generation of super computers. The two have an almost symbiotic relationship.

It began with the basic atomic theory and progressed to quantum mechanics which re-interpreted the behaviour of atomic and sub atomic particles. These theories gave the physical chemist the tools to build meaningful pictures of how molecules stretch, bend and move, governed by the behaviour of their electrons.

With the arrival of modern computers they were able to picture what might happen if they made the molecule slightly different or position its atoms in altered positions.

The idea is not limited to the structure of inorganic materials but it works with complex bio-chemical systems opening the door to new medicines and treatments for cancer.

The search for chemical truth has been the Holy Grail for chemists since they were alchemists, but now it is down to mathematical calculation. As Nobel Prize winning physicist Paul Dirac once said: “It’s more important to have beauty in the equations than to have them fit the experiment”.  The equations helped create the software and the software has unlocked infinite possibilities in all human activity from engineering to physiology and from genetics to computers.

British born chemist John Pople was also a Nobel laureate for his work in quantum chemistry, but his crowning achievement was in computer programming. His Gaussian programme was one of the first to help create accurate images of molecular structures. It is in effect a computational software programme to help us understand and visualise molecules.

These early programmes have become super sophisticated. With the Internet anyone can log on and view what a water molecule or a simple methane molecule ought to look like in digital form in three dimensions from every possible angle.  More significantly we have the maths to predict what might happen if these structures were changed in subtle ways to our advantage.

While water probably is one of the most studied and stable molecules on the planet, it’s interesting to surmise what might happen if you altered the stereochemistry of the oxygen-hydrogen bond in some way; could it make water behave in some way differently?

Water is perhaps not the best example of this idea, but when it comes to materials science we are using this technique across a vast range of materials. Among those at the leading edge in the field is Professor Emily Carter from Princeton University. Elected to National Academy of Sciences (NAS) in 2008, Carter is a chemist at heart, whose life’s work has been dedicated to merging quantum mechanics, applied mathematics and solid state physics.

[caption id="attachment_26632" align="alignleft" width="200" caption="Emily Carter"][/caption]

At Princeton this cross-disciplinary approach to science is everything. It’s what attracted Einstein there in the 1930s.

Carter said upon her appointment to the NAS: “Everything I do begins with quantum mechanics…the laws that govern behaviour, properties and structure of molecules and materials. It’s the electron distribution in these molecules that govern their properties and by the use of mathematics we can predict how they will behave in certain situations.

What does this mean at a practical level? The cool thing is that it is possible to develop a computer simulation to solve many problems in the development of lightweight metal alloys to make them lighter to incorporate in vehicles to make them more fuel-efficient.

Ask the man in the street what is the greatest human advance of the last 75 years…He would be unlikely to cite how we are on the brink of conquering the world of atomic and molecular structure

Computer simulations make it possible to look at fundamental properties that allow us to explore elementary processes which experimental work cannot reveal.”

So for example this type of work has contributed to the design of turbine engines for electricity generation and jet engines in aircraft. Turbine engines operate at temperatures above the melting point of the metal alloy from which they are made. To make the alloy survive it’s necessary to coat it with material with a melting point far above the melting point of the alloy and one that transmits as little heat as possible. Basically it’s a heat shield.

Carter said: “What quantum mechanical computer programmes give us is an insight into the modes of failure of the materials. We can turn that knowledge on its head and say ‘Okay, we know what causes them to fail at the atomic scale, what can we do to ameliorate this failure and what can we do to uncover the fundamental reason why certain elements extend the lifetime of the coating’?”

So does this spell the end for formal experimental chemistry? Are test tubes, condensers, Bunsen burners and chemists in white lab coats likely to disappear? The answer is an emphatic ‘no’.

In the new world of quantum simulation, we’ll need to re-enforce our knowledge and analyse outcomes and apply them to manufacturing use. We’ll be able to test the predictive nature of the quantum world.

But if ever the human desire to control the Universe took a one giant leap forward, it happened when quantum theory met the first modern computer. And it’s the quantum chemists who deserve the credit as we reap the vast benefits.

The Author: Dermot Martin

Dermot is a writer on Chemistry and media adviser for Bournemouth and Poole College