Recent Progress in Understanding Exact Conditions

We have seen in the previous two sections how knowledge of those exact conditions the LSD approximation obeys was vital to the construction and testing of PW91, and how its success relative to earlier GGA s can be attributed to these conditions. We believe that the construction of better functionals is intimately linked to improvements in our understanding of these conditions. In this section we present some results of more recent investigations, which were undertaken since the construction of PW91. 

This change is small, except for high densities and substantial gradients. Therefore we do not recommend the use of PWL in place of PW91. However, it should be noted that in some cases, this change can be important, e.g., there is a 10% change in the correlation energy of Ne. 

---