11 research outputs found
On the Meaning of Berry Force For Unrestricted Systems Treated With Mean-Field Electronic Structure
We show that the Berry force as computed by an approximate, mean-field
electronic structure can be meaningful if properly interpreted. In particular,
for a model Hamiltonian representing a molecular system with an even number of
electrons interacting via a two-body (Hubbard) interaction and a spin-orbit
coupling, we show that a meaningful nonzero Berry force emerges whenever there
is spin unrestriction--even though the Hamiltonian is real-valued and formally
the on-diagonal single-surface Berry force must be zero. Moreover, if properly
applied, this mean-field Berry force yields roughly the correct asymptotic
motion for scattering through an avoided crossing. That being said, within the
context of a ground-state calculation, several nuances do arise as far
interpreting the Berry force correctly, and as a practical matter, the Berry
force diverges near the Coulson-Fisher point (which can lead to numerical
instabilities). We do not address magnetic fields here
Non-adiabatic Dynamics in a Continuous Circularly Polarized Laser Field with Floquet Phase-space Surface Hopping
Non-adiabatic chemical reactions involving continuous circularly polarized
light (cw CPL) have not attracted as much attention as dynamics in
unpolarized/linearly polarized light. However, including circularly (in
contrast to linearly) polarized light allows one to effectively introduce a
complex-valued time-dependent Hamiltonian, which offers a new path for control
or exploration through the introduction of Berry forces. Here, we investigate
several inexpensive semiclassical approaches for modeling such nonadiabatic
dynamics in the presence of a time-dependent complex-valued Hamiltonian,
beginning with a straightforward instantaneous adiabatic fewest-switches
surface hopping (IA-FSSH) approach (where the electronic states depend on
position and time), continuing to a standard Floquet fewest switches surface
hopping (F-FSSH) approach (where the electronic states depend on position and
frequency), and ending with an exotic Floquet phase-space surface hopping
(F-PSSH) approach (where the electronic states depend on position, frequency,
and momentum). Using a set of model systems with time-dependent complex-valued
Hamiltonians, we show that the Floquet phase-space adiabats are the optimal
choice of basis as far as accounting for Berry phase effects and delivering
accuracy. Thus, the F-PSSH algorithm sets the stage for modeling nonadiabatic
dynamics under strong externally pumped circular polarization in the future.Comment: 40 pages, 4 figure
Total Angular Momentum Conservation in Ab Initio Born-Oppenheimer Molecular Dynamics
We prove both analytically and numerically that the total angular momentum of
a molecular system undergoing adiabatic Born-Oppenheimer dynamics is conserved
only when pseudo-magnetic Berry forces are taken into account. This finding
sheds light on the nature of Berry forces for molecular systems with spin-orbit
coupling and highlights how ab initio Born-Oppenheimer molecular dynamics
simulations can successfully capture the entanglement of spin and nuclear
degrees of freedom as modulated by electronic interactions
Practical Phase-Space Electronic Hamiltonians for Ab Initio Dynamics
Modern electronic structure theory is built around the Born-Oppenheimer
approximation and the construction of an electronic Hamiltonian H_{el}(X) that
depends on the nuclear position X (and not the nuclear momentum P). In this
article, using the well-known theory of electron translation (Gamma') and
rotational (Gamma'') factors to couple electronic transitions to nuclear
motion, we construct a practical phase-space electronic Hamiltonian that
depends on both nuclear position and momentum, H_{PS}(X,P). While classical
Born-Oppenheimer dynamics that run along the eigensurfaces of the operator
H_{el}(X) can recover many nuclear properties correctly, we present some
evidence that motion along the eigensurfaces of H_{PS}(X,P) can better capture
both nuclear and electronic properties (including the elusive electronic
momentum studied by Nafie). Moreover, only the latter (as opposed to the
former) conserves the total linear and angular momentum in general
A phase-space semiclassical approach for modeling nonadiabatic nuclear dynamics with electronic spin
Chemical relaxation phenomena, including photochemistry and electron transfer
processes, form a vigorous area of research in which nonadiabatic dynamics
plays a fundamental role. Here, we show that for nonadiabatic dynamics with two
electronic states and a complex-valued Hamiltonian that does not obey
time-reversal symmetry, the optimal semiclassical approach is to run surface
hopping dynamics on a set of phase-space adiabatic surfaces. In order to
generate such phase-adiabats, one must isolate a proper set of diabats and
apply a phase gauge transformation, before eventually diagonalizing the total
Hamiltonian (which is now parameterized by both R and P). The resulting
algorithm is valid in both the adiabatic and nonadiabatic limits, incorporates
all Berry curvature effects, and allows for the study of semiclassical
nonadiabatic dynamics in the presence of spin-orbit coupling and/or external
magnetic fields
Direct cloning and heterologous expression of the salinomycin biosynthetic gene cluster from Streptomyces albus DSM41398 in Streptomyces coelicolor A3(2).
Linear plus linear homologous recombination-mediated recombineering (LLHR) is ideal for obtaining natural product biosynthetic gene clusters from pre-digested bacterial genomic DNA in one or two steps of recombineering. The natural product salinomycin has a potent and selective activity against cancer stem cells and is therefore a potential anti-cancer drug. Herein, we separately isolated three fragments of the salinomycin gene cluster (salO-orf18) from Streptomyces albus (S. albus) DSM41398 using LLHR and assembled them into intact gene cluster (106 kb) by Red/ET and expressed it in the heterologous host Streptomyces coelicolor (S. coelicolor) A3(2). We are the first to report a large genomic region from a Gram-positive strain has been cloned using LLHR. The successful reconstitution and heterologous expression of the salinomycin gene cluster offer an attractive system for studying the function of the individual genes and identifying novel and potential analogues of complex natural products in the recipient strain