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CVP is usually recorded at the mid-axillary line where the manometer arm or transducer is level with the phlebostatic axis. This is where the fourth intercostal space and mid-axillary line cross each other allowing the measurement to be as close to the right atrium as possible.

a. Basic Concepts

The basic idea of DFT+U is that we are replacing the treatment of some of the charge density with a Hubbard correction term, where otherwise it would be treated by the chosen DFT exchange-correlation (XC) functional. This correction, in practice, is usually a screened Hartree-Fock-like term as opposed to being more reminiscent of the actual Hubbard model. A double-counting term is subtracted to remove the estimated contribution from the original XC functional. However, this term is not uniquely defined, so the choice of double-counting correction will affect the results. Most calculations use a fully-localized limit, most appropriate for strongly localized states.

DFT+U has the effect of introducing discontinuity in the total energy as a function of electrons added to the system--the rationale behind why it can improve the prediction of band gaps (if this is unclear, read on the band gap problem in DFT). In fact, the value of U can be defined in terms of this unphysical curvature present in LDA and GGA. A more intuitive interpretation of DFT+U can be illustrated by the form of the rotationally-invariant "simplified" correction (reducing explicit U and J terms to an effective $U_{\text{eff}}=U-J$) developed by Dudarev et al. and Cococcioni et al., where the Hubbard energy is minimized when orbitals in the Hubbard manifold are either completely full or empty, i.e. no partial occupations due to hybridization. This means there is a tendency to decrease delocalization in the calculation (compensating for how GGA, for example, tends to over-delocalize).

A more recent development is DFT+U+V, which includes inter-site interaction V and can improve the description of covalently-bonded materials.

I recommend reading this excellent review article by Himmetoglu et al. for an overview of DFT+U.

b. Constrained Random Phase Approximation

The constrained random phase approximation (cRPA), developed by Aryasetiawan et al., is used to find a frequency-dependent U that can be used in DFT+DMFT, but in the static limit it can be used in DFT+U. Essentially, once you have chosen how to define the localized and delocalized states for your system, the Coulomb interaction between the localized states is calculated while including screening effects from the delocalized states. The "constrained" comes from the fact that only the Hartree term is used to calculate the dielectric function used for screening, for simplicity (as opposed to both Hartree and exchange-correlation). I personally have not used cRPA to calculate values of U, so check the reference paper and its citations for further reading on the topic.

c. Linear Response

The linear response method by Cococcioni et al. defines U such that when applied the unphysical curvature in the total energy vs. the number of electrons present in the system is eliminated. In exact DFT this is a piecewise-continuous linear function, while in approximate LDA and GGA DFT it is a smooth curved function. Constrained DFT was an approach to correct this by varying the Hubbard orbital occupations, and determining the corresponding change in energy. Linear response approaches this in a more convenient way for most DFT codes, by applying a varying perturbative potential and then measuring the resulting change in occupation. Once this is done for several perturbations, U can be calculated (see resources section for how to do this). This approach typically requires U to be calculated in a supercell, to prevent the Hubbard states from being affected by periodic images of the perturbation.

d. Density Functional Perturbation Theory

A very nice recent development in the calculation of U is from Timrov, Mazari and Cococcioni. They reformulate the linear response method from a single perturbation in a supercell to a sum of perturbations in the primitive cell. I'm not as familiar with the theory here, but it's implemented in the new hp.x code included with Quantum Espresso. Very interesting.

d. ACBN0

ACBN0 (named for the authors) takes inspiration from previous work by Mosey and Carter, and explicitly calculates U from a Hartree-Fock-like interaction between the Hubbard orbitals of interest. Some screening-like reduction of the interaction is introduced by renormalizing the occupations of the Kohn-Sham orbitals according to their projectability on the Hubbard basis--so less-localized states should have a drastically reduced magnitude of U. This method also allows calculation of many site-dependent U values from a single scf calculation. In theory this can be incorporated into the self-consistency loop of the DFT calculation, but current implementations are a post-processing step. It can be used in the PAOFLOW and AFLOW$\pi$ codes. It's also been recently demonstrated with DFT+U+V.

a. References for Implementations of Hubbard U Corrections

b. Future Possibilities

A limitation of the simplified implementations of DFT+U is that the Hubbard orbitals are treated in a way that assumes some spherical symmetry (i.e. very close to true atomic orbitals). In compounds that have significant crystal field splitting this is not technically appropriate. Some early work used different U values for $t_{2g}$ and $e_{g}$ electrons in perovskite oxides, for example. The exchange term J is also treated in an average way, which worsens treatment of materials where the localization depends on Hund's rule magnetism. It could be very interesting to determine U, J and V for specific subsets of the Hubbard orbitals. This may provide better treatment of orbitally-ordered materials, or materials where some of the d electrons form an itinerant band (and should have a much smaller U value than the localized states, and may also participate in screening).

c. Practical Information/Tutorials

Check Following Video