In recent generalized Kohn-Sham (GKS) schemes for density functional theory (DFT) HartreeFock type exchange is important. In plane waves and grid approaches the high cost of exchange energy calculations makes these GKS considerably more expensive than Kohn-Sham DFT calculations. We develop a stochastic approach for speeding up the calculation of exchange for large systems. We show that stochast...

The electrical response of molecular chains is dramatically overestimated by local and semilocal density functionals. We show that Kohn-Sham density-functional theory yields accurate linear and nonlinear polarizabilities when the exact exchange energy is employed together with the corresponding exact Kohn-Sham potential upsilonx(r). We further show that approximations to upsilonx(r) that are ve...

We solve the long-standing problem of the large overestimation of the static polarizability of conjugated polymers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation (xc) effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory en...

The description of economic behavior as sequential decision making under uncertainty has been hampered by the limited nature of the available theoretical results. This paper tries to fill some of the gaps. In particular, the paper develops some basic results for the problem of search. We present a general formulation of the search problem in Section 2. Search is seen as sequential sampling from...

We have recently presented a real-space method for electronic-structure calculations of periodic systems that is based on the Hohenberg– Kohn–Sham density-functional theory. The method allows the computation of electronic properties of periodic systems in the spirit of traditional plane-wave approaches. In addition, it can be implemented efficiently on parallel computers. Here we will show that...