Thursday, May 28, 2015

NF - mysteries of a small molecule

Nitrogen fluoride (NF) seems like a very simple molecule and you would think it would very well understood, particularly as it is small enough that it is accessible to high level quantum chemistry calculations. However, the molecule exhibits some subtle properties that present a theoretical challenge. There is limited experimental data because the molecule is only found as an intermediate in some chemical reactions.

Just like oxygen (O2), to which it is isoelectronic, the ground state is a triplet due to Hund's rule, as discussed for O2 here.

I just read a nice paper
A Valence Bond Study of the Low-Lying States of the NF Molecule 
Peifeng Su, Wei Wu, Sason Shaik, and Philippe C. Hiberty

Given that F is more electronegative than N one might expect the ground state to have a large electric dipole moment and this to increase as the molecule is stretched.
However, the ground state has only a small moment, it has the opposite direction to that expected from the electronegativity, and the direction changes sign when the bond is stretched.

Furthermore, unlike most molecules, the bond length is shorter and the dissociation energy larger in the low-lying excited states [which are singlets] than in the ground state.

The ground state has one sigma bond and six electrons in two pi orbitals.
The latter form three-electron bonds, which in the Valence Bond picture, involve exchange in position of an electron pair and an unpaired electron, where one goes from T1 above to the configurations shown below.
The authors consider 9 valence bond structures for the triplet ground state and 12 singlet VB structures for the two lowest singlet states. Their calculations lead to the following picture in terms of Lewis structures.

What insights are gained by the VB approach? Key is the idea of back donation or back bonding.

In a nutshell, the three lowest-lying states of NF can be considered as primarily bonded by a polar two-electron σ bond, complemented by π-bonding contributions of the three-electron bonding type for the ground state, and of the classical two-electron type for the excited states. In all three cases, the π-bonding contributions correspond to charge transfer from F to N, thus counterbalancing the σ polarization by back-donation. The tendencies of the bond lengths in the various electronic states comply with this simple model. Thus, all the computations and experimental measurements show that the bond length decreases consistently from the 3Σ state to 1Δ, and from 1Δ to 1Σ+. This counterintuitive tendency, which implies that the more excited the molecule is, the more strongly it is bonded, is easily explained by the weights of the π-bonding Lewis structures, that sum up to 19 % in 3Σ state, to 28 % in the 1Δ state, and to 37 % in the 1Σ+ one (Figure 1 and Table 1 and Table 3). The same increase in the π-bonding contribution accounts again for the unusual fact that the bonding energy is far larger in the first excited state than in the ground state (96.4 vs 72.0 kcal mol−1 at the VBCISD level). On the other hand, the bonding energy of the second excited state is now smaller than that of the first, as expected, since both excited states dissociate to the same products.

The tendencies in the dipole moment values of the various states are also readily rationalized by the simple VB model. The polar σ bond tends to tip the electron density towards the fluorine atom, and thus to favour negative values of the dipole moment (in the direction N+F), while backdonation from the π systems has the opposite effect. The two effects compensate for each other in the ground state, where backdonation is moderate (19 % of π charge transfer). In the 1Δ state, as the π charge transfer is increased relative to the ground state (28 % vs 19 %), backdonation wins over σ polarization, leading to a significant positive dipole moment, in the direction F+N. The effect is further reinforced in the 1Σ+ state, in which the π-charge transfer Lewis structure has such a large weight (37 %) that it completely overwhelms the σ polarization, ending up at a positive dipole moment of 0.728 D at the BOVB level.
I would like to see a basic description of these essential features in terms of a polarised two site Hubbard model with multiple orbitals and Hund's rule coupling, generalising the unpolarised two-orbital model here.

I got interested in this paper because of thinking about improper hydrogen (and halogen) bonds and wondering whether there is an "excited" diabatic state that has a shorter and stronger X-H bond than in the ground state. A general "ionic" (X^-H+) state will not have this property but if there is the option of back donation maybe something can happen....

Wednesday, May 27, 2015

Justifying pure science research: Discovery

How do you convince politicians to fund basic research?

On The West Wing there is an episode Dead Irish Writers in which many things are happening simultaneously. One is that Sam Seaborn [White House Deputy Communications Director] is meeting with a Princeton Physics Professor, Dr. Millgate who is dying of cancer but trying to secure funding for the Superconducting Super Collider. It features the following excellent dialogue.

Sam Seaborn: Okay. I said I'd do this, but it's likely he's gonna say this is an unaffordable luxury. 

Millgate: We're losing the race for discovery, Sam. For discovery. Tonight, it's just me and you. 

Sam Seaborn: That doesn't really sound like enough. 

Millgate: No.

Then in a later scene

Senator Enlow: If only we could only say what benefit this thing has, but no one's been able to do that. 

Dr. Millgate: That's because great achievement has no road map. The X-ray's pretty good. So is penicillin. Neither were discovered with a practical objective in mind. I mean, when the electron was discovered in 1897, it was useless. And now, we have an entire world run by electronics. Haydn and Mozart never studied the classics. They couldn't. They invented them. 

Sam Seaborn: Discovery. 

Dr. Millgate: What? 

Sam Seaborn: That's the thing that you were... Discovery is what. That's what this is used for. It's for discovery.

Is this why in Australia the main source of research grants for people like me are "Discovery Grants"?

Tuesday, May 26, 2015

John Nash (1928 - 2015): a founder of game theory

John Nash and his wife, Alicia, tragically died in a car crash on the weekend. There is a New York Times obituary He was a brilliant young pure mathematician who laid foundations for game theory in a 27 page Ph.D thesis. Nash became widely known outside academia through the movie A Beautiful Mind, that tells his life story, focusing on his struggle with severe mental illness. It is based on an excellent biography by Sylvia Nasar. It is less sanitised than the Hollywood version.

Tragically Nash's life also illustrates the importance of mental health issues in academia, and so I mention him in talks I give about mental health for scientists.

I have a strange personal connection with Nash. When I was a graduate student at Princeton I often saw a middle aged man reading Scientific American in the Maths/Physics library. He was often there and I wondered why he was there. Didn't he have a job? Yet I don't remember ever asking anyone about him. Also, sometimes in the Physics building there were strange scribblings all over the chalk boards.

One day in 1994 I got a shock when I received a copy of The Princeton Alumni Weekly. There on the cover was a photo of the man I often saw in the library with the headline "John Nash wins Nobel Prize in Economics". Finally I found out who he was and learnt his story.

Friday, May 22, 2015

Advice for undergrads giving research talks

At UQ all physics honours students (4th year undergrad) have to give two 15 minute talks about their year long research project. The first is a progress report at the end of the first semester and the second at the end of the project. No grades are given for these presentations but they are attended by the 3 thesis examiners [supervisor, expert, and non-expert] and so may influence the grade for the thesis.

I think these presentations are very challenging for the students and I am sometimes impressed at the quality of the talks. This is a great opportunity for students to develop and improve their communication skills. When I was an undergrad we never had opportunities like this. Most of us also had very little public speaking experience. Students today are quite different and much more confident and polished.

Here is my advice to students.

First, review general material on giving scientific talks such as Garland's Advice to Beginning Physics Speakers or Wilkins' one page or Geroch's suggestions or Mermin's. Don't think you know better than these old timers.

Second, decide on your audience [your friends, other students, faculty, your research group, the examiners?]. I hate to say it but the examiners is the correct answer.
Taylor the talk accordingly.

Third, decide on your real goal [impress others, show how much work you have done, show off how much jargon you have learnt, be entertaining, talk about how great your research field is, make excuses for your lack of results....?].
Taylor the talk accordingly.

The goals of the progress seminar are simple.
Show you have a well defined and realistic project.
Show you have a clear plan.
Show you have started to make some progress.

The goal of the final seminar is simple.
Show you have achieved something concrete and worthwhile.
Anything else is subsidiary.

Be realistic about how much you can achieve in 15 minutes.
Some background is crucial but don't let it dominate your talk.
Don't spend more than a minute about why the research field is important and interesting.
Don't spend more than a minute on the history of the field.
Don't think you can explain how Shor's algorithm works, the subtleties of the quantum measurement problem, or the microscopic basis for Landau's Fermi liquid theory, ...
Most of the talk should be about what you have done and why it is significant.
Yet, if you can teach people one small thing they will be very appreciative.

Clearly distinguish between the contributions of founders of the field, those of your supervisor, and yourself.
Include relevant references on your slides.

Avoid irritants: being late, having problems with the technology, small fonts, endless jargon, hype, lavish Powerpoint animations, .....

Practise. Practise. Practise.
Consider writing out explicitly what you are going to say.

Start preparations early. Get feedback.

How you answer the questions is important.
Listen carefully. Don't cut off the questioner.
Don't bluff an answer. Saying you don't know is o.k.

Relax. The audience knows that this is a stressful experience, particularly for the inexperienced, and does not expect a perfect talk.

Thursday, May 21, 2015

A unified picture of weak chemical bonds: hydrogen, halogen, carbon...

Previously I posted about improper hydrogen bonds. These are weak hydrogen bonds that have the unusual property that in the X-H...Y system H-bonding leads to a shortening and hardening (blue shift) of the X-H bond. In contrast, for "proper" bonds, X-H lengthens and softens (red shift).

The past few years has seen a rapid increase in interest in an even broader class of weak bonds such as "halogen bonds",  denoted X-Z...Y where Z can now be not just H but a halogen (F, Cl, Br), chalcogen (O, S, Se, Te), or pnictogen (N, P, As, ..)....

There is an interesting paper that contains the helpful summary figure below
Negative hyperconjugation and red-, blue or zero-shift in X-Z---Y complexes
Jyothish Joy, Eluvathingal D. Jemmis and Kaipanchery Vidya

In trying to understand the paper I found reading the following older paper helpful
Electronic Basis of Improper Hydrogen Bonding:  A Subtle Balance of Hyperconjugation and Rehybridization
Igor V. Alabugin, Mariappan Manoharan, Scott Peabody, and Frank Weinhold

[Aside: note the senior author is Weinhold who has featured in some previous posts]

The basic idea is that there are two competing interactions. "Hyperconjugation" is Weinhold's view of proper H-bonds, via the Natural Bond Orbital donor-acceptor picture where the H-bond arises due to charge transfer from the lone pair orbital on Y to the σ* (anti-bonding) orbital associated with X-H. This lengthens and hardens X-H.
When this interaction is weak there is “X-H bond shortening” due to increase in the s-character (rehybridisation of the atomic orbital on X) and polarization of the X−H bond. This is associated with a shorter and harder X-H bond.

Bent's rule is central. It is one of the most general rules governing structure of organic molecules.
atoms tend to maximize the amount of s-character in hybrid orbitals aimed toward electropositive substituents and direct hybrid orbitals with the larger amount of p-character toward more electronegative substituents.
Increasing s-character generally leads to shorter bonds.
As the donor acceptor distance (X-Y) decreases the X-Z bond becomes more polarised and the s-character increases.
The authors note it should be possible to test predicted trends since the amount of s character in the X-Z bond can be measured from the relevant NMR coupling constant.

My question is whether this subtle competition can be captured by generalising my simple 2 diabatic state model for H-bonds to a 3 state model that includes the ionic character of the X-Z bond.

Tuesday, May 19, 2015

Measuring the viscosity of the electron fluid in a metal

Previously I posted about the theoretical issue of the viscosity of the electron fluid in strongly correlated metals. This interest is partly motivated by claims from string theory techniques [AdS-CFT] that there is a universal lower bound for the viscosity.  A recent experimental paper estimated the viscosity in the cuprates by an indirect method from ARPES data.

I only became aware recently that there is a somewhat direct way to measure the viscosity of the electron fluid in a metallic crystal. This has a long history going back to Mason and Pippard who in 1955 related the viscosity to the attenuation of sound. A more sophisticated and general theory was developed by Kahn and Allen.

The connection between shear viscosity and ultrasound attenuation can be loosely motivated as follows. In a viscous fluid the attenuation of a shear wave is given by Stokes law

where \eta is the shear viscosity of the fluid, \omega is the sound's frequency\rho is the fluid density, and V is the speed of sound in the medium.

This equation has been used to determine the shear viscosity as a function of temperature for helium three [a correlated neutral fermion fluid]. Extensive experimental data is reviewed here.

In a metal, provided the wavelength of sound is much larger than the electronic mean free path, then one is in the hydrodynamic limit, and the attenuation is given by a similar expression to that above (with appropriate indices for crystal axes), with \rho the solid density (not the electron fluid).

One can show from the Boltzmann equation that in a simple free electron model that the electronic viscosity is proportional to the scattering time, just like the conductivity. Hence, the ultrasound attenuation should scale with the conductivity.

Indirect evidence for this idea is from the data below that shows the temperature dependence of ultrasound attenuation of aluminium (taken from here).

In clean metals, such as for the data shown above, the attenuation [and viscosity] becomes very large at low temperatures, making it easier to measure.
Also, for high frequency ultrasound, one can reach the "quantum regime" where the mean free path becomes comparable to the sound wavelength. Pippard worked out a general theory describing the crossover from the hydrodynamic regime to this quantum regime.

In bad metals could one experimentally see the small viscosity, of the order of n hbar [where n is the density]? First, the small mean free path, characteristic of bad metals, means one will always be in the hydrodynamic regime. However, the small viscosity means that the sound attenuation due to the electron fluid will be small and possibly dominated by other sources of attenuation such as crystal dislocations. A rough estimate for an electron viscosity of order of n hbar and a sound frequency of 1 GHz gives an attenuation of less than 0.1 cm-1, of the order of typical sensitivity, such as in these measurements for heavy fermion compounds.

Friday, May 15, 2015

What is real scientific integrity?

According to the Oxford English Dictionary Integrity = "The quality of being honest and having strong moral principles".

When people talk about scientific integrity and misconduct they mostly have a narrow definition which means "don't make up data."

However, I think we need to consider a broader definition of integrity that relates to all communications and messages.

Scientists talk about their research in a wide range of forums:
  • private discussions
  • articles in luxury journals
  • articles in professional society journals (PRA, JCP etc)
  • grant applications and job applications
  • seminars at universities and conference presentations
  • press releases and interviews
  • public lectures and popular books
Yet it seems it has now become quite acceptable to have different messages (claims and conclusions) in different forums. This post was stimulated by a perceptive comment by Steve W on a previous post.
My finding is if you talk to the authors of luxury papers with controversial or sexy explanations, that they will be the first to admit their own skepticism regarding their explanations of the data. But somehow this skepticism is not conferred to the text, because the luxury journals like clear, concise, authoritative explanations. Most of the details get hashed out later in less prominent, but longer form journals, and these are only followed closely by those within the specific community. 
For a concrete example see a recent post by Peter Woit about the basic question, "Is string theory experimentally testable?" He highlights a significant inconsistency between the answers in a preprint, the published version in PRL, a press release, and a public talk by Amanda Peet.

Thursday, May 14, 2015

From a spin liquid to a correlated Dirac metal

There is an interesting paper
Theoretical prediction of a strongly correlated Dirac metal 
 I. I. Mazin, Harald O. Jeschke, Frank Lechermann, Hunpyo Lee, Mario Fink, Ronny Thomale, Roser Valentí

The compound Herbertsmithite ZnCu3(OH)6Clhas attracted a lot of interest because it is a Mott insulator with a layered crystal structure where the Cu2+ ions (spin 1/2) are arranged in a kagome lattice.
There is some evidence both experimentally and theoretically that the ground state is a spin liquid.
[However, inevitably there are complications such as the role of impurities and the Dzyaloshinskii-Moriya interaction].

In this paper the authors replace the Zn2+ ions with (isoelectronic) Ga3+ ions. This means that in non-interacting electron picture the bands go from half filling (n=1) to two-third filling (n=4/3). This is of particular interest because for a tight-binding model on the kagome lattice there are symmetry protected Dirac points, just like in graphene, at this band filling.

There are subtle interlayer effects because the kagome layers order ABCABC....
This changes the three-dimensional Bravais lattice from hexagonal to rhombohedral and a doped system will have a Fermi surface like that below.

However, one needs to take into account the strong interactions associated with the localised Cu orbitals that lead to a Mott insulator at half filling. The authors use a range of theoretical techniques (rotationally invariant slave bosons, functional RG, Dynamical Cluster Approximation (DMFT)), to investigate instabilities in the associated Hubbard model.
They find a subtle competition between metallicity, charge ordering, ferromagnetism, and f-wave superconductivity.

Hopefully, someone will make this compound soon!

I thank Ben Powell for bringing the paper to my attention. He and Anthony Jacko recently considered an organometallic material with a rich band structure that interpolates between honeycomb and kagome.

Tuesday, May 12, 2015

The challenging interface of science, policy, and politics

Last week I went to an interesting talk What are the effects of dredging on the Great Barrier Reef?
by Laurence McCook, at the Global Change Institute at UQ.

I went because I knew Laurence in my undergraduate days at ANU. In first year we had all the same lectures, tutorials, and labs. (I guess groups were assigned based on the alphabet.) We became friends and he introduced me to many beautiful places for bushwalking [backpacking] and cross country skiing near Canberra.

There is a piece on the Conversation that gives a brief summary of the issues associated with the report from the expert panel that Laurence and  Britta Schaffelke co-chaired. Basically, it involved a "cat herding" exercise with 17 experts from industry, government, and universities. I am always impressed by people who manage such enterprises and can produce concrete useful outcomes. I think it requires considerable patience, political skills, and leadership. 

A helpful figure is below.
Aside: it would be interesting to try and do an exercise like this for topics such as cuprate superconductors, topological quantum computing, water, glasses, quantum molecular biophysics......

So what effect does dredging have?
Specifically, which of the effects is most likely to do the greatest environmental damage?

It seems that the ongoing turbidity [cloudy water] and sedimentation associated with sediment dynamics could be the biggest problem. But, this is also one of the most poorly understood processes. 
The figure below summarises some of the complex processes involved. Modelling this presents a major challenge (and some interesting science).

A problem with these exercises where science meets policy meets politics, particularly on controversial issues, is that they can highlight uncertainty and the general public does not like that. Science is meant to be certain. People want black and white answers. "Dredging is harmless and we should not worry about it vs. Dredging is an environmental disaster and should be banned".

It is interesting that of "10 scientific ideas that scientists wish you would stop mis-using" the first is Proof.

Friday, May 8, 2015

Holon-doublon binding as the mechanism for the Mott transition

What is the mechanism of the Mott metal-insulator transition?
After 50 years this remains a debated issue.

A number of distinct mechanisms for the transition have been proposed. These include those due to Brinkman and Rice (where the quasi-particle weight in the metallic phase approaches zero as the transition is approached), Hubbard (where vanishing of the charge gap occurs when the upper and lower Hubbard bands overlap), or Dynamical Mean-Field Theory (DMFT) which combines both these features.

My collaborators and I discuss an alternative mechanism in a paper that we just finished.

Holon-Doublon Binding as the Mechanism for the Mott transition
Peter Prelovsek, Jure Kokalj, Zala Lenarcic, and Ross H. McKenzie
 We study the binding of a holon to a doublon in a half-filled Hubbard model as the mechanism of the zero-temperature metal-insulator transition. In a spin polarized system and a non-bipartite lattice a single holon-doublon (HD) pair exhibits a binding transition (e.g., on a face-centred cubic lattice), or a sharp crossover (e.g., on a triangular lattice) corresponding well to the standard Mott transition in unpolarized systems. We extend the HD-pair study towards non-polarized systems by considering more general spin background and by treating the finite HD density within a BCS-type approximation. Both approaches lead to a discontinuous transition away from the fully polarized system and give density correlations consistent with numerical results on a triangular lattice.

Two things I found (pleasantly) surprising in this study were:

-two "simple" analytical approaches (retraceable path approximation and a BCS-type variational wave function) seem to capture much of the essential physics.

-one can learn quite a lot by approaching the problem from the highly (spin) polarised limit.

We welcome comments and suggestions.

Thursday, May 7, 2015

Battling High Impact Factor Syndrome II

Last friday we had a great colloquium at UQ from Carl Caves on High-impact-factor syndrome: What, why, and what to do.

Much of the talk followed Carl's article The High-impact-factor syndrome on The Back Page of the American Physical Society News. I posted about it before.

Here are a few new things that emerged.

Reinhardt Werner had a nice piece in Nature, The focus on bibliometrics makes papers less useful. The comments and his responses are worth reading.

Last week Nature published The Leiden Manifesto for Research Metrics.

Nature Publishing Group has launched the Nature Index to rate individuals, departments, institutions, and countries. They claim it is a "global indicator of high quality research". It is based on only 68 journals, including many NPG journals! For example, the only APS journals included are PRL and the Rapid Communications parts of PRA, PRB, and PRD. Journal of Chemical Physics is not included. There are no mathematics journals.
I find this enterprise rather disturbing.

One needs to consider not just the Impact Factor which is a mean (average) but rather the width and the shape of the distribution.
For example, for Nature Physics, the bottom 50 per cent have 7 citations/paper/year. This is the same as the impact factor for PRL. Hence, even if you believe in such citation measures, half of the Nature Physics papers are really just like a PRL!

What are some of the problems with HIF syndrome?

Campbell's law will come into play.

"The more any quantitative social indicator (or even some qualitative indicator) is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor."

Gaming the system is inevitable.

Scientists surrender their research agenda to the Editors of Nature.

There is a tendency toward short, punchy, "hit and run" papers.

There is a trend towards hype and salemanship and fluff. This means a reduction in the commitment to the search for truth and scientific integrity, two things that set science apart as a social enterprise.

Tuesday, May 5, 2015

Not seeing the pseudogap in ultra cold 2D atoms

Two weeks ago it was nice to have Meera Parish visit UQ and give a colloquium Fermions in Flatland. She recently moved to Monash University from University College London.

One important point she made was the comparison of the two figures below, showing a colour intensity plot of the one fermion spectral function A(E,k) for a two-dimensional Fermi gas near the unitary limit (BCS-BEC crossover).

The bottom figure is experimental data from a Nature paper, 
It makes much of the possible connection to the pseudogap seen in cuprate superconductors.

The top figure is from a theory paper
Vudtiwat Ngampruetikorn, Jesper Levinsen, and Meera M. Parish
Therefore, our results suggest that the observed pairing gap [Nature paper] effectively arises from two-body physics and does not correspond to a pseudogap regime. This view is further supported by the fact that the pairing gap in the spectrum persists to very high temperatures well above Tc, as shown in Fig. [above]. Moreover, we see that the “closure” of the gap with increasing temperature appears to be due to the thermal broadening of the two branches.
An earlier post discussed more recent measurements of the spectral function in three-dimensional ultra cold fermionic atoms near the unitary limit.

Friday, May 1, 2015

The challenge of setting priorities

We all have limited time, energy, and money.
We all have priorities even if we can't clearly state them or don't publicly state them.
Setting priorities is a challenge not just for individuals but also for departments, institutions, and research fields.
I think rarely does this happen well.

When priorities are not clearly stated, whether from individuals to institutions, "stake holders" are left trying to guess and speculate what the priorities really are.

Publicly stated priorities too often look like a "dog's breakfast": a mishmash of wish lists from competing interests, or a laundry list...

I feel this sometimes applies to lists of "research strengths" or "research priorities" that  Australian universities come up with every few years.

Every few years departments in Australian universities are extensively reviewed, leading to a list of 20-30 specific recommendations, that the department chair is then held accountable to implement before the next review. However, these recommendations seem to be given equal weight whereas they really may vary significantly in their importance and value.

Another example are the Sustainable Development Goals from the United Nations, which are the successor to the eight Millennium Development Goals. In spite of their many faults I think the MDGs had merits and did lead to some significant outcomes. But, the SDGs (17 goals with 169 targets) may lead to no significant outcomes due to their breadth, as critiqued by The Economist.

Because condensed matter physics and chemistry are diverse and diffuse fields I think they can suffer in the funding game, particularly in some countries, when you have competing interests that will publicly (or privately when reviewing grant proposals) put each other down. In contrast, some fields such as high energy physics and astrophysics are sometimes very good at bringing their community together to privately agree on priorities and then publicly lobby for support, particularly for large projects.
I think a recent exception for condensed matter is that finally the community has agreed that growth of high quality single crystals of quantum materials is a long-neglected priority, something that the Moore Foundation has picked up on.

Do why don't we set priorities?

It is hard work.

It involves incomplete information where the future is uncertain.
We don't know what projects or people are going to be fruitful in the long term.

It may involve the painful process of saying no.
We have to say no to many good things in order to realistically pursue a couple of excellent goals.
Sometimes it is time to quit and cut our losses.

Some people will be disappointed and/or get offended.
They and/or their pet projects may not be a priority.
This is particularly why often real priorities are not clearly stated or when they are they are a "dogs breakfast".

We are waiting for a miracle to happen.
If all of the sudden we got a big breakthrough on the project, or a new big grant or a brilliant student or something else things would become easier and simpler.

Having said all this, I think having set the priorities is just the first challenge. Sticking to them in the face of setbacks, changing circumstances, criticism, and discouragements can be an even greater challenge.

So, how do you set priorities? If not, why not?
Should chemistry and condensed matter be more clearly setting priorities? Is that politically realistic?