Saturday, July 31, 2010
Thursday, July 29, 2010
- Ehrenfest mean-field dynamics
- Surface hopping
- Ehrenfest + decoherence (Prezhdo, Rossky, Schwartz...)
- Semi-classical dynamics (Miller–Meyer–Stock–Thoss formalism)
- Partial Wigner transforms (Kapral)
- Multiple spawning
- Full nuclear quantum dynamics
Wednesday, July 28, 2010
Monday, July 26, 2010
Sunday, July 25, 2010
Saturday, July 24, 2010
Assumption*:for the ground to excited state transition in the chromophore the transition dipole moment is much smaller than the difference of the dipole moments between the ground and excited states.
- the absorption and emission lines obey the mirror image rule
- in the "high" temperature limit (which is reasonable for most solvents at room temperature) the line width is proportional to the Stokes shift and to the temperature
- the reorganisation energy is much less than the transition energy[this just means one can clearly resolve the absorption and emission bands]
- the solvent degrees of freedom are treated classically.
Friday, July 23, 2010
In recent years, the EVB has become a widely used tool in the QM/MM modeling of reactions in condensed phases and in biological systems, with ever increasing popularity. However, despite the fact that its power and validity have been repeatedly established since 1980, a recent work (Valero, R.; et al. J. Chem. Theory Comput. 2009, 5, 1) has strongly criticized this approach, while not discussing the fact that one of the authors is effectively using it himself for both gas-phase and solution studies. Here, we have responded to the most serious unjustified assertions of that paper, covering both the more problematic aspects of that work and the more complex scientific aspects. Additionally, we have demonstrated that the poor EVB results shown in Valero et al. which where presented as verification of the unreliability of the EVB model were in fact obtained by the use of incorrect parameters, without comparing to the correct surface obtained by our program.
Thursday, July 22, 2010
Wednesday, July 21, 2010
uncontrolled photocharging of the nanocrystal core can lead to exaggeration of the Auger decay component and, as a result, significant deviations of the apparent [carrier multiplication] CM efficiencies from their true values. Specifically, we observe that for the same sample, apparent multiexciton yields can differ by a factor of 3 depending on whether the nanocrystal solution is static or stirred.
Tuesday, July 20, 2010
Monday, July 19, 2010
Saturday, July 17, 2010
(i) the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far;
(ii) all observed ‘‘restrictions’’ can be correctly and comple
tely accounted for by taking into account environmental decoherence effects;
(iii) no positive experimental evidence exists for physical state-vector collapse
"Ohhhhhhh. ... Look at that, Schuster. ... Dogs are so cute when they try to comprehend quantum mechanics."
What are the assumptions in this minimal theory?
First, a completely known (pure) state of an isolated quantum system is described by a normalized state vector in a Hilbert space.
Second, the time evolution of a state vector is given by the time-dependent Schrodinger equation.
No mention is made of measurements in this formulation. Instead, measurements are described without special axioms in terms of physical interactions between systems described by state vectors (wave functions) and governed by suitable interaction Hamiltonians. Observables then emerge as a derived concept.
Basically, I agree with these and it is nice to see the arguments set out so clearly. On the other hand, I don't follow some of Max's arguments about the amount of entanglement in the macroscopic states that he discusses.
Friday, July 16, 2010
Thursday, July 15, 2010
Wednesday, July 14, 2010
Tuesday, July 13, 2010
The Dimensions of perfectionism
• Excessive concern about making mistakes
• High personal standards
• Perception of high parental expectations
• Perception of high parental criticism
• Doubting of the quality of ones actions
• Preference for order and organisation
An interesting study [which may have never been cited!] I found in ISI but not online claims "Surprisingly, graduate students may procrastinate on academic tasks even more than do undergraduate students. Perfectionism also has been found to be high among graduate students."
Monday, July 12, 2010
Saturday, July 10, 2010
Friday, July 9, 2010
A very effective way to start learning what computational chemistry can and cannot do is to start doing hands on tutorials of concrete examples. Last week, at the I2CAM workshop on photovoltaics, Jeff Reimers ran a hands on workshop where participants calculated photochemical properties associated with charge separation and recombination in a specific donor-acceptor molecule. Here is the tutorial sheet and you can run Jeff's CNDO (Complete Neglect of Differential Overlap) [something like a Hubbard model..] code on the nanohub.
Thursday, July 8, 2010
The fact that exciton states may be delocalized among chromophores is obviously interesting and implies quantum communication between them, provided it survives decoherence effects due to the surrounding medium. One could then justifiably argue that the chromophores are entangled and that the dynamics is profoundly quantum in nature. However, as shown here, these quantum effects can be easily eliminated by basing the description on the delocalized exciton modes.
by Bredas, Norton, Cornil, and Coropceanu.
"Only wimps study the general case. Real scientists work through examples."
I thank Ben Powell for bringing the quote to my attention.
Wednesday, July 7, 2010
This year the School will again employ a webcast system that allows for real-time streaming of video/audio of its proceedings, including all the lectures, questions, answers, and discussions.
Tuesday, July 6, 2010
Monday, July 5, 2010
To what extent does computational chemistry actually guide drug design?
This came up in the previous post concerning "virtual screening" of candidate molecules for organic photovoltaics.
Seth Olsen brought to my attention a nice article, Virtual Screening: an endless staircase, by Gisbert Schneider that appeared earlier this year in Nature Reviews Drug Discovery. Here is part of the abstract:
Computational chemistry — in particular, virtual screening — can provide valuable contributions in hit- and lead-compound discovery. Numerous software tools have been developed for this purpose. However, despite the applicability of virtual screening technology being well established, it seems that there are relatively few examples of drug discovery projects in which virtual screening has been the key contributor.
Furthermore, the article says:
Substantial progress in virtual screening requires a profound understanding of the forces that govern protein folding and the dynamics of macromolecular complex formation.
The figure above is taken from a this paper about the action of aspirin.
Sunday, July 4, 2010
Saturday, July 3, 2010
Friday, July 2, 2010
At the conference today, my colleague Seth Olsen gave a talk Stucture-Property Relationships for Conjugated Organic Dyes.
Thursday, July 1, 2010
- What is the mechanism of charge transport?
- What is the origin of the observed electric field dependent mobility?
- What determines the relative magnitude of electron and hole mobilities?
- How does mobility depend on the intermolecular separation and relative orientation?
- Would thermopower measurements be helpful in determining the charge transport mechanism?