RAS SCF,

The major problem with the CASSCF method is the limited number of active orbitals that can be used. However, one notes in many applications that some of these orbitals will have occupation numbers rather close to two for the whole process one is studying, while others keep low occupations numbers. The restricted Active Space (RAS) SCF method was developed to handle such cases [15, 24], Here, the active space is partitioned into three subspaces RAS1, RAS2, and RAS3 with the following properties ... 

The CAS(RAS)SCF method is one of the best methods to study excited states and photochemical processes because it can in a balanced way treat closed and open shell electronic states of varying complexity and also of different spin, which is necessary in studies of intersystem crossing. However, calculations on excited states is often more complicated than those for a well defined ground state. Preferably,... 

The number of active orbitals that can be used in a CASSCF calculation is limited. Some problems needs larger active spaces than can be used today. It is then possible to use a less general way to construct the wave function, for example, the restricted active space (RAS) SCF method [79]. Such methods can use larger active spaces, but there exist no corresponding RASPT2 program yet. Such a code would be of great value. 

Figure 1 3. Contour plot of the electron density of CO, showing the magnitudes and directions of atomic and charge transfer dipoles (arrow length is proportional to magnitude). Arrow heads point to the negative end. The molecular dipole moment is given by the vector sum of charge transfer terms (p.c.t.) and the atomic polarizations ( ra p). Values were obtained at the DFT level using the B3LYP functional and the 6-31 1+G(3df) basis set. The SCF molecular dipole = 0.096 D the computed molecular dipole ( Jtc.t.[0] + Aa.p.[0] + Hc.JC] + Aa.p.[C]) = 0.038 au = 0.096 D, close to the experimental value of 0.1 10 D (15).

There are two types of parameters that determine the RAS wave function the Cl coefficients and the molecular orbitals. When both of them are optimized the result will be a RASSCF (CASSCF) wave function, which is a extension of the SCF method to the multiconfigurational case. Below we shall briefly show how the optimization is done in practice in most modern programs (more details can, for example, be found in Ref. [25]). 

Stem cell factor (SCF) and its receptor c-kit play an important role in hepatocyte regeneration and proliferation. APAP treatment results in increase SCF and the c-kit receptor expression in liver beginning at 6 h. Pathways activated by SCF include PI-3 kinase, Src family members, JAK/STAT, and Ras-Raf-MAPK cascade (Hu and Colletti 2008). SCF administration hours after APAP treatment resulted in increase hepatocyte proliferation and a reduction of APAP-induced liver injury. SCF treatment increased bcl-xl and bcl-2 expression in liver mitochondria,... 

Some neuroblastoma cells overexpress the c-Kit receptor for its ligand, stem cell factor (SCF), and release SCF in an autocrine loop for self-stimulation of mitoses. Imatinib mesylate suppresses PDGF and tyrosine kinase c-Kit (GDI 17) expression. Somatostatin inhibited PDGF-induced phosphorylation of PDGFR and inhibited ras gene amplification. For local invasion, these tumor cells release MMP2/9. The synthetic MMP inhibitor, prinomastat, suppresses MMP production and tumor cell locomotion. However, MMP expression is promotional for neuroblastoma cell differentiation. The presence of MMP is necessary for the neurite formation of retinoic acid-treated neuroblastoma cells neurite formation is the first sign of differentiation induction (vide infra) [1624]. 

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