799 research outputs found
Hybrid RHF/MP2 geometry optimizations with the Effective Fragment Molecular Orbital Method
The frozen domain effective fragment molecular orbital method is extended to
allow for the treatment of a single fragment at the MP2 level of theory. The
approach is applied to the conversion of chorismate to prephenate by chorismate
mutase, where the substrate is treated at the MP2 level of theory while the
rest of the system is treated at the RHF level. MP2 geometry optimization is
found to lower the barrier by up to 3.5 kcal/mol compared to RHF optimzations
and ONIOM energy refinement and leads to a smoother convergence with respect to
the basis set for the reaction profile. For double zeta basis sets the increase
in CPU time relative to RHF is roughly a factor of two.Comment: 11 pages, 3 figure
DiffEnc: Variational Diffusion with a Learned Encoder
Diffusion models may be viewed as hierarchical variational autoencoders
(VAEs) with two improvements: parameter sharing for the conditional
distributions in the generative process and efficient computation of the loss
as independent terms over the hierarchy. We consider two changes to the
diffusion model that retain these advantages while adding flexibility to the
model. Firstly, we introduce a data- and depth-dependent mean function in the
diffusion process, which leads to a modified diffusion loss. Our proposed
framework, DiffEnc, achieves state-of-the-art likelihood on CIFAR-10. Secondly,
we let the ratio of the noise variance of the reverse encoder process and the
generative process be a free weight parameter rather than being fixed to 1.
This leads to theoretical insights: For a finite depth hierarchy, the evidence
lower bound (ELBO) can be used as an objective for a weighted diffusion loss
approach and for optimizing the noise schedule specifically for inference. For
the infinite-depth hierarchy, on the other hand, the weight parameter has to be
1 to have a well-defined ELBO
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