What is the Psychological explanation of raskolnikov's four-day delerium?

Nihilism was a philosophical position developed in Russia in the 1850s and 1860s, known for “negating more,” in the words of Lebezyatnikov. It rejected family and societal bonds and emotional and aesthetic concerns in favor of a strict materialism, or the idea that there is no “mind” or “soul” outside of the physical world. Linked to nihilism is utilitarianism, or the idea that moral decisions should be based on the rule of the greatest happiness for the largest number of people. Raskolnikov originally justifies the murder of Alyona on utilitarian grounds, claiming that a “louse” has been removed from society. Whether or not the murder is actually a utilitarian act, Raskolnikov is certainly a nihilist; completely unsentimental for most of the novel, he cares nothing about the emotions of others. Similarly, he utterly disregards social conventions that run counter to the austere interactions that he desires with the world. However, at the end of the novel, as Raskolnikov discovers love, he throws off his nihilism. Through this action, the novel condemns nihilism as empty.